It is currently moving in he direction of a more federal system like the US.

The big reasons are

• greater migration between Wales and England than between England and Scotland (just by virtue of geography),

• greater political nationalism in Scotland (rather than Wales' more cultural nationalism),

-the fact that Wales has for around 500 years been legally part of England.

Here is the history:

Wales has legally been part of the Kingdom of England since the 1534 Act of Union. (I think it is legally separate since in 1997 it got its own govt. etc) This Act of Union was not really a union of equal partners. It was an annexation.

In 1603, the King of Scotland also became the King of England. This is called a union of crowns. Both kingdoms remained separate, the same person, King James simply ruled both, as James VI of Scotland and as James I of England.

James tried to roll the two kingdoms into one, but this was resisted on both sides. So for 100 years, the two kingdoms remained separate, each with their own constitutions and Parliaments.

By 1700, both sides were more used to one another and wanted Union -England liked not having to worry about an enemy to the north, and wanted to make sure that no European rival would take the throne of Scotland. The Scots grew to like and depend upon England's more sophisticated economy and financial institutions. Both sides hated and feared Catholicism.

So in 1707, there was an Act of Union, but it was a union of equals: the Kingdom of Scotland and the Kingdom of England ceased to exist, and were replaced by the United Kingdom of Great Britain.

Scotland retained a number of powers in this new union, most notably retaining their own legal system, Scots Law. This is a crucial part of why Scotland and England/Wales are different .

In the 18th century, the nation building project proceeded apace - there was a Scottish Enlightenment, with notable philosophers like Hume, but interestingly, all of these guys were embarrassed of being Scottish, and styled themselves as 'British' at a time when England was very focused on 'Englishness'.

In the late 19c., Scottish nationalism started to emerge. I'm not an expert on this, but I understand that it largely started as a bit of a joke, e.g. the whole Tartan thing was reinvented to try to impress a visiting Queen Victoria.

Through the 19c., Wales was populated by a lot of English migrants to the valleys. I don't think this happened on the same scale in Scotland, where migrants were mostly Scots or Irish.

The decline of the Empire in the early 20c. IMO really put a strain on Scotland's place in the union - for 300 years it was one of the few shared institutions Scots really had a big part in - Scots were frequently the shock troops of Empire, whether in the military or as settlers (see for example Appalachia and the Southern US).

By the late 20c. Welsh nationalism had emerged as a way to ensure the survival of the language and culture. But it never became a strong political nationalism because of how much inter-migration there had been between Wales and England. Scotland, because of it's location, never had the same mass migration to and from England (the borderlands of Northern England are fairly empty)

I think some of the responses here are slightly inaccurate and as both a British person (with some natural knowledge of this) and someone who has studied the Act of Union I thought I would add my own version.

Wales was annexed by England in the 1270s and 1280s, although it was not officially incorporated as part of England until the 1500s. In short though, whilst not officially part of the Kingdom of England, in all practical respects it has been for the last 700 years or so. This meant for many of the most important periods of institution building, the two countries were united. The common law system developed in both countries. The elites of England were largely transplanted into Wales (even if the populace remained quite distinct, successfully maintaining their own language etc. better than the Scots). When the English reformation rolled around, Wales was part of that process. Even when Wales later developed its own religious identity of non-conformism in the 18th Century it still built upon this Anglican tradition focusing on Methodism (a movement with its roots within the Church of England) rather than other forms of Protestantism. Even today, the Welsh Assembly has FAR fewer powers than the Scottish Parliament.

In contrast, Scotland remained separate for far longer. They were entirely separate until 1603 when James I/VI became King of England. Up to this period a large number of the distinct institutions of Scotland had developed. In particular Scotland had developed a civil law legal system, its own Presbyterian Church and its own educational system and institutions in the form of Universities such as St. Andrews. In the 17th Century there were some fitful starts at integration. Notably both Charles I, and Parliament in the Civil Wars attempted to ally with the Scots. Scotland was integrated as one polity (with representation in the Westminster Parliament) during the Protectorate of Oliver Cromwell right up until the restoration of the Monarchy.

When the Act of Union was formed it was in the context of the Glorious Revolution and fears that James II and France might try and use division between the nations to aid an invasion. Scotland had also seen its economic position worsen, and in particular a disastrous attempt to set up a colony around modern day Panama had backfired. However, it was clearly a voluntary union (unlike the one with Wales) and thus Scotland kept many of its independent institutions: its own Church, its own legal system, its own educational system.

As well as this I would contend that Scottish nationalism benefited from the 18th and 19th Century ideas of the 'noble savage' and romanticism. Most Scottish people lived in the lowlands and came from Anglo-Saxon roots, and all the ideas we now associate with 'Scotland' were in fact entirely Highland and Gaelic. Historically most Scots would have rejected the facets of clan society as barbaric. However, the Gaels, like the native Americans, were viewed as noble savages even whilst their genuine culture and society was wiped out in the 18th Century. This period also interestingly saw the development of tartan and kilts (an excellent overview of this can be found in 'Invented Tradition' by Eric Hobsbawm). It also saw the development of a mythology around it with books such as James McPherson's 'Works of Ossian'. This new form of Scottish identity was further expanded in the 19th Century until everyone basically forgot how recent and artificial it was. Even today, Scottish nationalism is far more strongly felt than Welsh nationalism. The Scottish Parliament has more powers and in a lot of ways Scotland remains far more distinct.

TLDR: Wales was integrated earlier and did not retain as much of a distinct identity. Scotland had a much longer time to develop its own institutions, and maintained them better, as well as benefiting from romanticism and other fetishisations of highland culture and thus has maintained a much stronger nationalism and a more distinct polity.

Further, why do the Scots speak English, having a historically tenuous relationship with England, and the Welsh speak... well, Welsh?

This is interesting. Just a few quick questions.How did the Norman Conquest of England affect the Welsh ?

The Tudors were Welsh too.

What would be the closest American concept to think of the various British nations, are they treated like American states or more like the various member nations of the EU?

While a lot of people like to see the European Union as some sort of emerging supranational federation, by definition it's more akin to a confederation then anything. The difference being that while a federation is a political union of self-governing states, a confederation is a union of sovereign states that seek a common front on principles (the European Union being a historically economic one).

The closest (nation-wide) political concept that Americans share with the British devolved Parliament system is the current federal system that the United States (a form of governance also found in a number of other countries including Canada, Germany, and Russia). I point out nation-wide as there is an actual closer American comparison but ill get to it later.

As you may have noted federation is pretty much a union of partially self-governing states. While the British nations have self-governance and a degree of autonomy akin to a federal system, it isn't a true federal system as these self-governing rights are not entrenched in any form of constitution (and thus those rights are not guaranteed). The local parliaments of Scotland and Wales were parliaments granted by the Parliament of the United Kingdom, and can be revoked at any time by that same Parliament. So what place In United States actually operates in a nearly identical manner? The District of Columbia.

Like the British devolved Parliament system, The District of Columbia has a form of devolved governance granted by the Congress. This can also be taken away by Congress noting the fact that the District has no reserve constitutional powers.

As to soccer leagues, Berwick Rangers, a club in an English town, play in the Scottish League, for reasons of simple geography. They are farther north than several Scottish teams they play against and only just south of Glasgow Rangers and Celtic.