WHOOHO! A bunch of nations just joined the Axis powers, because of the random invasion of neutral Spain! And America loses the home front war like they did in Vietnam! And everyone stopped trusting allies!
There was one nation in Europe in WWII the Western Allies could have attacked with only minimal political costs: Fascist Spain. Spain was not a genuine neutral, it had co-belligerent status on the Eastern Front through the employment of the Blue Division, with some 80,000 troops overall being employed from start to finish. There is your
Casus belli right there.
The only other "neutral" country the Western Allies could have attacked was the Irish Free State, and only before France fell, with a weak Casus belli (Dublin dropping its treaty obligations) against a democratic country and facing US hostility for it that would have rendered Lend-Lease or any US entry stillborn short of OTL events.
Neutrality was an issue. Spain didn't join in in 1940 when Britain had it's back to the wall. To violate Spanish Neutrality would mean other nations in future wouldn't trust the W/Allies to abide by the standards they set for themselves.
This is the Ostensible reason.
Spain under Franco was thoroughly Fascist, it's an apologia for Fascism to deny that.
Agreed
Now for the actual reason, beyond the fact that it would have been much like Italy, a long slow slog through mountainous terrain with poor infrastructure, sucking up shipping in providing food for the population..
Was that the W/Allies supported Franco from the beginning. Officially they (1) were neutral, in practice they allowed covert shipments of Oil to Franco's side in the civil war. They were -
1. Taking care of their investment interests in the country,
2. Suppressing revolution against Capitalism in Europe.
Recall how Truman made that comment (2) about getting Nazi Germany & the Soviet Union to face off against each other & destroy each other? That was the sentiment of the late-30's/early-40's.
1) Who were "they"?
2) Source?

Because a statement like that made by Truman in the 30s or early 40s would have made him a very unlikely VP candidate for FDR in 1944, and a gift that would never stop giving for Soviet propagandists throughout the Cold War. God knows, they never stopped reminding us that British Prime Ministers Stanley Baldwin and Neville Chamberlain said it.
Germany/Italy wanted the advance of Fascism, a place to test their methods of war. The Soviet Union sold weapons for Spain's gold reserves & then sold out the revolution (seized the logistics in the Rebel rear areas, arrested anyone who wasn't on their side & went on to lose the war) in order to placate the W/Allies whose industrial equipment they were buying.
I thought that had to do with Stalin's pathology about doing his utmost to purge the ranks of communist parties that were (due to geography) beyond his means under normal circumstance to kill?
Would you mind re-phrasing the highlighted section? The way its written makes it look as if NATO existed in the 1930s. Are you saying that the USSR was buying industrial equipment from the West? The "W/Allies" as such didn't exist during the Spanish Civil War.
Spain in WW2 relied on Oil shipments from the U.S. Hitler had none to spare. There was monitoring by the W/Allies of what went in & what went out of the country to make sure none went to Germany. The U.S leaned towards going to war, (3) the U.K leaned against it as it was afraid Spain would nationalize U.K investments in a period where they were going into massive debt.
3) Just who exactly in the USA wanted to go to war with Spain?

American Communists? It certainly wasn't FDR, or the US State, War, or Navy Departments.
There were still rebel Guerrillas operating in country in Spain in 1944. An invasion by the W/Allies might have left them in control of some of their home ground. That would have been a major threat to the W/Allies, their propaganda was based around them being the saviours of freedom. Those rebels would have viewed them as oppressors like they did the Fascists & likely have eventually fought with them for local control.
Like all the other (including Italian) partisans did?

I know the Greek partisans did, but they were actual Communists fighting mostly postwar and receiving direct overland support from the supply lines of the Red Army. The Spanish partisans, whose position by this time was hopeless, would have ITTL have been in a worse position to fight the W/Allies than the Communist French during the Liberation of France.
This is why Spain became a NATO member post war, not another target for the Allies.
Uh, Spain didn't join NATO until 1982, eight full years after Franco's death, and thirty seven years after the guns fell silent in Europe.
Yep, although I suspect that if enough money were tabled, Franco might just be amenable, his demands to Hitler for entering the war were beyond what the Germans could afford to pay, but could the Americans have paid it?
I don't even want to THINK about what ALT AH posters would have to say about the USA having given all that $$$ to Ferdinand Franco.
I don't think that in 1944 Spain was in any shape to oppose resistance to the advance of the Allies, if they decide to land in Spain. It wouldn't be Italy. It wouldn't even be Poland, it would be Denmark. (4)
4) A strategic dead end with nightmarish LOCs, weak supply sources, poor infrastructure (for force needs) and a strategic bottleneck at the end? Yep, JUST like Denmark.
I think it's way more likely that, being informed of the landing, Franco decided to have Spain join the Allies, and the WAllies would find themselves suddenly on the Pyrinees already. Maybe Franco could be forced to stage some sort of token resistance, and then accept defeat and Allied control.
After all, seeing the tide changing Franco hadn't been shy about saying that in the conflict between Germany and the WAllies, he sided with the WAllies.
I don't see the W/Allies doing an invasion without a DoW and proper political buildup, in which case Franco will be under irresistible pressure to grant the Germans right-of-passage in Spain, thereby nullifying the Allied advantage of the soft underbelly strategy, as OTL. Italy underwent over three long years of defeat, loss of their empire and Sicily before they surrender, and when they tried to effect a switching of sides, they politically collapsed. Spain, when being invaded while at peace and NOT having directly attacked the Western Allies is going to fight, and fight hard. They will certainly neither switch sides nor rapidly surrender.
On the whole, though, after having attacked Italy and getting stuck there, a landing on France was the best option. But if we were still on 1943, i think Spain would have been a better choice than Italy (in hindsight).
Attack Italy, and the Central Mediterranean is cleared, freeing up enormous amounts of Allied shipping (far fewer Cape of Good Hope convoys) and knocks a major Axis power right out of the war. Invading Spain adds one.
