I read that the Nazis supported the nationalists during the civil war , what was the thinking? And why wasn't Spain able to join the war on the axis side?

I'm currently reading The War of the Three Gods by Peter Crawford which details Islam's rise during the seventh century. It seems like before almost every battle, the Muslim commanders would use their specially-trained mubarizun to duel officers of the opposing army to kill as many of them as possible and undermine their enemy's moral. Would these duels be expected by both sides in seventh century battles, or was this a new tactic the Muslims developed?

I have several Republican friends who pride themselves in being financially conservative; that is, they don't align with the more religious side of the right on social issues, but admire old Republican financial policies. That said, I can't help but find it odd how much attention and praise Reagan gets as the "hero" of modern Republicans (in fact, the level of praise I see him get is nearly on the level of fervor). It is in my limited understanding that Reagan's economic policies cost America far more than Obamacare (e.g. the War on Drugs), and that Reaganomics is a failed economic theory (as evidenced by America's ever-growing super-rich to poverty gap). So why the love and hero worship?

What tactics and equipment did the early muslims use when they expanded their caliphate?

My History teacher told me that a lot of historians don't agree to the 1947-1991 dates of the Cold War. When do you think the Cold War started and why?

I'm primarily thinking bout western society

As a follow up, I would also like to know how the suit came to be a dominant formal wear in today's society.

Such as Jorvik. What type of buildings did they have? What was the general appearance of these major town?

What led to the prevalence of diesel engines in personal vehicles in Europe as opposed to the United States where the petrol engine is almost exclusive? Were there any benefits to the use of one or the other and if so, do these still benefits still exist today?

If I recall correctly, this was a time period when Europeans knew about and used firearms, but when said firearms were not useful enough to replace earlier weapons like bows. So my question is: how big of an investment would this be for an individual? I recognize that these sort of prices would vary from region to region and that it would be far easier for individuals of certain classes of society to buy them, but I'm more looking for a general idea of value, rather than exact numbers. Thanks for your assistance.

I know Connolly wrote about nationalism but was it stemmed solely from the pursuit of democracy and anti-imperialism or was he just very patriotic / anti-British?

Can it be determined from his and other writings that the Irish independence movement would have been satisfied if an international socialist movement had come about, perhaps including Britain and Ireland under one banner e.g. in the event that a British socialist state had been established that wanted to retain its bonds with Ireland?

In reading about the Pelopennesian wars I read the account of the athenian defeat in Sicily and the selling of captured soldiers into slavery. If I were a captured soldier sold into slavery would I plan to never see my family again? Was the institution of slavery in ancient Greece different to more modern notions of slavery as seen in the African slave trade to the Americas?

Is there any historiographical debate regarding the issue or are historians (moderately) unified on the topic of prohibition?

And was this done intentionally to make it easier to preserve native heritage sites?