I think that the debate about the foreign policy of Lyndon Johnson is interesting because of how crucial this argument is in the debate over LBJ's entire legacy (since his foreign policy failures have so far eclipsed his domestic successes such as the Civil Rights Bill, Medicaid, etc.). Traditionally, historians and other analysts of foreign policy have given Johnson a very bad grade. This traditional view portrays Johnson as a president largely ignorant of world affairs who stumbled into Vietnam because his advisers convinced him that the United States could easily defeat Communism there, when in reality the Vietnam War had neither a clear path to victory or discernible purpose. His failure in Vietnam has become the defining feature of his presidency.

In recent years, however, historians have looked at components of his foreign policy overshadowed by Vietnam in order to construct a narrative much more favorable to Johnson (here I am thinking of works like Alan Schwartz's Lyndon Johnson and Europe and John Dumbrell's President Lyndon Johnson and Soviet Communism). Focusing on Europe and the Soviet Union, these historians concede that Johnson utterly failed in Vietnam but proved more nuanced in his approaches to Europe and the Soviet Union--areas that were truly key to American interests at the time. And Johnson did have some important successes in these areas. He maintained the NATO alliance despite challenges from both De Gaulle and the US Congress, he negotiated and signed the Nuclear Non-proliferation Treaty, and he laid the groundwork for future arms reduction talks with the Soviet Union, to name some of the most important ones.

My own master's thesis aims at contributing to this debate by highlighting Johnson's incompetence in handling the "Czechoslovak Crisis" created by the Prague Spring of 1968. I argue that Johnson's ineptness during the Prague Spring, an event at the crossroads of his European and Soviet policies, corroborates the traditional narrative that Johnson lacked the ability to enact an effective foreign policy for the United States.

Medieval heresies, especially the 'Cathars'.

Our received wisdom on a lot of history regarding persecution, inquisition and heresy in Medieval Europe has changed since the mid twentieth century. Even having left a history department fairly recently, I came across the full gamut of thinking on the Cathars, be they a vibrant and blossoming community, a niche or anomaly which was subsequently exaggerated and/or a complete fabrication.

The term itself; its scope, meaning and reach, are retrospective attempts at categorization themselves.

The minutia involved in interpreting the evidence we have on Cathars and other heresies from this period have filled half a dozen entire careers, so it might not be a perfect starting point for the more casual, but it is a fascinating and evolving topic.

If you are interested, R. I. Moore is a current heavyweight in the field and his books will be invaluable to you.

Edit: Formatting.

The most interesting debate in my field is about the origins of capitalism. There were a number of different theories that looked at the question "why did Europe develop capitalism before other world regions?" Some more savvy researchers tried to answer the more specific question "why did England develop capitalism before any other country in Europe?" But none of the researchers looking into these questions had a well researched global historical methodology. That is to say, they didn't really know that much about other regions of the world, such as China, and their discussions of culture, religion, social structure, etc., in those countries, was not very good.

So until recently, it was common for historians to say that there was something special about Roman Law or Christianity (or Protestantism) that simply made for a better environment for self-sustaining capitalist growth. With regard to England, there were a number of arguments about the social or class structure of the country, especially in the countryside, as compared to other European countries, but these arguments hardly made reference to non-European examples. In any case, these sorts of arguments all have to be rethought now because this sort of "Eurocentric" argument is no longer acceptable (which isn't to say that people don't think capitalism started in Europe; it's that they don't accept arguments about this that fail to really examine what was going on outside of Europe).

Really influential here have been current events: East Asia was once the richest part of the world, and now, it is becoming very wealthy again. People are doing more comparative work on the histories of China and England to try to solve this paradox: if China was so much wealthier than England around say 1500, why didn't China develop capitalism first? The renewal of this debate has been going on for a while now, since the early 2000s, but with the further, rapid expansion of the Chinese economy, the debate continues to develop.

I don't actually agree with this book, but it is a good summary of the best ideas in the field, in trying to answer this question: "The Origins of the Modern World" by Robert Marks, now in its 3rd edition.

In Post-Roman Britain, we're trying to figure out what the hell happened in the fifth century. Did barbarians invade Britain from Anglia and Saxony? Did the economy collapse? Did the legions actually withdraw in 410, or did Britain limp along as a marginal Roman province longer? Were there large political structures, or was everyone so poor that they had to focus on subsistence lest they starve? And why did this all seem to change rather abruptly c. 470/480?

We've had a ton of new archaeological discoveries, and are using new scientific methods to analyze these finds, but so far it's not solved any of these questions. We know that people did immigrate from Germany, but how exactly this happened, and what the experience was like for the people who lived through it, isn't clear - was it an invasion, or a slow peaceful process? A series of low-scale invasions and displacements? Normal population movements accelerated by the breakdown of Roman economic and political structures? Or an insignificant process that only became important centuries later when warring 'Saxon' and 'Welsh' kingdoms needed to invent a historical reason for whybthey hated each other so much?

And this is all complicated by the problem of chronology. We struggle to date things in the fifth century, partly because archaeologists have long assumed that anyting Roman is from before 410, and anything medieval after 450, and we've only recently started to recognize that a lot of things actually overlapped across this gap. But how, precisely, this overlap works out is very difficult to say because we don't have coins, texts, or inscriptions with dates on them, and radiocarbon dating is extremely imprecise during the fifth century due to some crazy sunspot activity that messed up the ratios of c14 in the atmosphere (all radiocarbon dates from the fifth century look basically identical).

So there's been a lot of productive work questioning our understanding of this period, but we're far from solving it. It's an exciting, if frustrating, puzzle to tackle.

Early seventeenth-century theology in the English (court) church. There are skeptics who question whether England truly had a reformation or not. Some of that has to do with the influence of Luther and Calvin and the emergence of the "Anglican" church as a middle road that later resembles the Catholic church, minus the pope.

I recently wrote my master's thesis on the sermons of Lancelot Andrewes (a really interesting preacher -- he was one of King James's favorite court preachers and did a lot of work on translating the King James Bible; TS Eliot has helped cement a somewhat misleading legacy due to a limited understanding [his and, until the past two decades or so, ours] of his works [due to a limited selection made available for publication])... Regardless, he's often been seen as kind of a founding father, along with Richard Hooker, of what would be called Anglo-Catholicism (a conservative wing of the Anglican Church)

Anyway, I don't know if this necessarily the debate of the pre-Anglican, English Church, but there's the so-called Tyacke thesis that identifies a group of "anti-Calvinist" reactionaries (mostly preachers) who responded to the Calvinist majority of the late Elizabethan/early Jacobean church that were a major influence in regards to the English Civil War. One debate is that of terminology: anti-Calvinists, Arminians, Laudian, Anglican -- are all terms used by historians to talk about this group but none is quite accurate (Anthony Milton recently wrote an article whose title lists all of them and asks the question: back to which drawing board?). Part of their theology was an emphasis on early Church fathers (both Latin and Greek) and English reformers, while largely, supposedly, ignoring continental influences. This perception was in part due to their being so against Calvinism (though many historians tended only to focus on predestination) that the preachers supposedly ignored anything from the continent (yet one of the movement's titles is Arminian...). This has led to multiple (British?) scholars talking about the "strange death of Luther" (Alec Ryrie, among others) in England -- arguing that after 1545 or so, Luther's influence disappeared from England. However, scholars of the anti-Calvinist preachers have mentioned that Laudian theology resembles Melancthon-influenced Lutheranism. One Andrewes scholar has recently written about discernible traces of Luther's theology of the cross in Andrewes's court sermons. So it's interesting to see the theological influences at the turn of the 17th century. Though the cynical question is -- what does it matter that all these brands of theology (Calvinism/Puritanism, Lutheranism, "Anglicanism") exist if you could still put them together as Protestantism that are more alike in their anti-Catholic measures...

Sorry for rambling -- but basically there's a lot of questions about how unified the "English church" was before the civil war.

There's an important debate currently going on about the relationship between slavery and capitalism with which I'm just endlessly fascinated.

Many highly regarded recent works basically argue that capitalism, particularly 19th c. American capitalism, required slavery in order to develop. (Ed Baptist's The Half Has Never Been Told, Walter Johnson's River of Dark Dreams, and Sven Beckert's Empire of Cotton are the most important recent works.)

I have some reservations about this position, and am interested to see how other scholars push the debate forward. In short, it seems that most of this scholarship conflates capitalism and industrialization, based largely off what I see as a misreading of Eric Williams' work. Many of the new works on slavery and capitalism openly eschew definitions of capitalism - I heard one high level scholar who shall remain nameless claim that we don't need definitions because we know capitalism when we see it, while another recently claimed that "slavery and capitalism are not different things." Its as though the important work by British scholars in the mid-20th century who located the capitalist transformation in the English countryside in the 15th century don't exist. (Here Maurice Dobb, Paul Sweezy, and the Brenner debates remain crucial, though it appears few off the new slavery and capitalism scholars have even read this work.)

Obviously, there is an important linkage here, but we're not likely to be able to measure the significance of slavery to the American economy by looking solely at the South. Cotton may have been crucial to the export market, but if nearly all of it was leaving the country, how important could it really have been to the dynamic growth of the North? And when we recall that cotton exports made up no more than 6% of GDP, assertions like those made in this new scholarship that ALL white Americans benefitted from slavery are a bit harder to support. I worry that sometimes the aim of this work is more to establish the "radicalism" of its author and the impliedly equal complicity of all Americans, North and South, living and dead, in the great crime of slavery. So in short I think looking at the connections between slavery and capitalism is maybe the most exciting debate going on in American history right now, but I want us to be very careful about what we mean by capitalism.

For a really excellent review of much of this literature, check out the review article by James Oakes in the most recent issue of International Labor and Working Class History - it makes these points better than I ever could.

Well, I'd imagine some people would find the Manx Rebellion during the English Civil War to be very interesting since it's a region that doesn't really turn up in mainstream study of the Civil War. The debate around what the major cause of the rebellion was - be it long term grievances with the Lord of Mann or the imminent threat of English invasion - is quite interesting to take part in.

I'd recommend reading Illiam Dhone: Patriot or Traitor? By Jennifer Draskau for a good overview of the period and an examination of both Illiam himself and how he is perceived today by the local people.

Not so much my field as one that I've done some work in, but there's an ongoing and interesting debate within the history of the American West about defining what we mean when we talk about "the West".

Is "the West" defined by the colonial frontier, whose location varies depending on the decade and can start around the Appalachian mountains? Is "the West" a fixed location defined by a shared set of environmental conditions (mostly centered around aridity)?

Other fields might debate about specific issues within the geographic and chronological era they specialize in - historians of the west also have to debate which geographic and chronological era their whole field specializes in.