The limitations on declaring war render democratic countries and factions to a more reactive role than the Fascists and Communists who have a lot more liberty in declaring war. When world tension reaches 100%, the democracies of the world can intervene and pick their sides.
The question is... in real life, the prominent democracies stood against the Axis even if it meant an alliance with the Communists. In HoI 4, we know it's also possible for democracies to stand with the German Reich against the Red Menace, or even face a combined Commie-Nazi alliance without a lesser evil to help them. But what dictates which, if either, of the two ideologies Allies side with? If I want to play Japan with a primary focus on defeating the Soviets and no particular desire to join the Germans or fight the Allied nations, what can I do to make World War II about destroying the communists instead of stopping fascism?
The question is... in real life, the prominent democracies stood against the Axis even if it meant an alliance with the Communists. In HoI 4, we know it's also possible for democracies to stand with the German Reich against the Red Menace, or even face a combined Commie-Nazi alliance without a lesser evil to help them. But what dictates which, if either, of the two ideologies Allies side with? If I want to play Japan with a primary focus on defeating the Soviets and no particular desire to join the Germans or fight the Allied nations, what can I do to make World War II about destroying the communists instead of stopping fascism?