I would say that Imperialism overlaps Fascism, but (one of the) difference(s) between the two is that Fascism goes a lot harder into Ultranationalism. Under Imperialism you have a King or Queen, and they are ordained by God to rule. Under Ultranationalist Fascism your race (or whatever they count as ‘race’, nation, etc) is what makes you superior to everyone else. It was a lot harder to get people to fight for Kings and Queens they only knew from coins, than to say “we’re fighting those EVIL (other nation people), whereas we are the PURE nation.”

Another difference is that Fascism adores and requires total war. Imperialism wants to expand, but Fascism wants to dedicate every aspect of the nation towards that goal. There’s that enigmatic ‘other’ that has to be destroyed, because it is both a weak and strong opponent. Fascism also says ‘violence is good for the nation, if directed properly.’ This means your January 6’s, your political assassinations, etc, are all highlighted as good things. ‘Drain the swamp’ kind of rhetoric becomes literal violence to allow people being killed.

As mentioned below, Franco’s Spain was quite bizarre, in that it had a lot of different traits (including fascist ones).

Imperialist nations can abandon overseas colonies, ‘let’ them become independent, etc. Yet Fascist nations need invasion and war to keep their economy going, which means they have to pick bigger fights. They also relied on slave labour (and I’m going to take this opportunity to name and shame the corporations that used those people as slave labour:

Among the slave laborers in the occupied territories, hundreds of thousands were used by leading German corporations including Thyssen, Krupp, IG Farben, Bosch, Blaupunkt, Daimler-Benz, Demag, Henschel, Junkers, Messerschmitt, Siemens, and Volkswagen, as well as the Dutch corporation Philips.

What people forget about Germany is that they had always planned to invade the Soviet Union. There’s a lot of talk about ‘if they hadn’t,’ but their lebensraum plan required it. In 1944 75% of their economy went to the military. They’d been deficit spending every year since the early/mid 30’s. Fascism requires that all effort be put towards the military and war, regardless of if you’re at war, but you need to be at war to get the land/money/etc you need to pay for the military that you made to… etc.

So anyway yes, fascist nations bully countries until either a bunch of them or one big one puts them back down.

Historians debate just how fascist Franco was. Hell, Orwell wasn’t even quite sure, and he was very open about the fact that he went to Spain to kill a fascist.

Edit: a choice passage out of Homage to Catalonia, emphasis added:

But there were several points that escaped general notice. To begin with, Franco was not strictly comparable with Hitler or Mussolini. His rising was a military mutiny backed up by the aristocracy and the Church, and in the main, especially at the beginning, it was an attempt not so much to impose Fascism as to restore feudalism. This meant that Franco had against him not only the working class but also various sections of the liberal bourgeoisie—the very people who are the supporters of Fascism when it appears in a more modern form. More important than this was the fact that the Spanish working class did not, as we might conceivably do in England, resist Franco in the name of ‘democracy’ and the status quo; their resistance was accompanied by—one might almost say it consisted of—a definite revolutionary outbreak. Land was seized by the peasants; many factories and most of the transport were seized by the trade unions; churches were wrecked and the priests driven out or killed. The Daily Mail, amid the cheers of the Catholic clergy, was able to represent Franco as a patriot delivering his country from hordes of fiendish ‘Reds’.

And as a side note, the Daily Mail has been terrible for a long, long time.