> That's fair, but wouldn't you say that the coup was made possible by the fourth constitution's bad design and not really attributable to the country's being a democracy?

There’s no way to design a constitution on paper to avoid the risk of a military coup, especially not if you want to keep an effective military at the same time. Civilian control of the military is an institution that needs to established with generations of indoctrination. The United States has done an unusually effective job of this, which would come as a happy surprise to our founders, who feared the inherent risks of a standing army.

1958 is also a little late to try and cast blame on the circumstances of the Second World War. The coup had more to do with the fact that the democratically elected government of France was willing to allow Algerian independence and the military was not. Algeria was still lost in the end, but the military was more willing to accede to the personal authority of De Gaulle rather than the institutional authority of the elected government.

> The question is, was loss in mainland France avoidable or not?

Yes. France had more and better tanks than the Germans at the start of the war and a large enough army that, if properly used, they could have effectively defended their country. Even the surprise of Germany’s incursion through the Ardennes could have been countered if not for blunders on the part of the French.

> France was defeated extremely quickly, so the choice the government had wasn't between "fight to keep the current republic" and "collaborate", but more between "lose the mainland and go resist from abroad" and "abandon control of the mainland to the Nazis and collaborate"

Algeria wasn’t an overseas colony of France; it was just as much a part of France as Lyon or Bordeaux. And as I pointed out earlier, France didn’t even lose control of all of the “mainland” until Germany reacted to Darlan’s sudden shift in loyalty in 1943.

Most countries that were conquered by Germany maintained governments in exile rather than willingly collaborate. France’s government was an exception to this rule, though Britain did what it could to establish the fiction that De Gaulle represented a “government in exile”, and since Germany eventually lost the war, that fiction became a more palatable narrative for France’s wounded national pride. That’s not what actually happened though.

If the Republican government actually stood firm against Germany and was forced out of Europe and into Algeria until it could, with the help of its allies, recover its territory, I might agree with your argument that it’s not fair to consider 1940 the end of French democracy. The problem is that the military defeat in 1940 and the transformation of the Third Republic into an autocracy were largely products of French internal politics. The French cabinet and military did not value or respect either their democracy or their alliance with Britain, with many of them of the attitude that they should have sided with the Germans all along. At least, until the Germans started losing. Even then, relations with Britain were strained to the point that the United States had to manage the alliance from Torch onward.