@david-06 While I certainly agree on that, I also just don’t think letting one alliance build up unchecked won’t end well either!
My typical play/hope is to use my lightning war round effectively in the west to take at least all of France, though hopefully Norway, Denmark, Belgium, and the Netherlands as well.
In doing this, you wrap up mainland resistance right away, and the UK is almost assuredly in no position to make amphibious assaults against you immediately after, allowing you some time to build defenses, while focusing more manpower in the east.
Depending on how the game has gone to this point (i.e. where my troops have been placed, enemy troops are placed, peacetime income increase rolls, etc.) I will also either simultaneously attack the USSR, utilizing the Lighting War and Soviet Surprise Attack abilities, and hopefully getting to the two front line cities/factories quickly.
To me, doing this now neutralizes any big French buildup of units in France. The longer it takes to take them out, the harder and more costly it’ll be, and the more IPP’s you’ll have to sacrifice taking them out will hurt! But I think you have the larger IPP advantage at this point in having gained French IPP (and money in the bank), and now France was taken out efficiently, while also making any UK attempts much more costly with amphibious assaults instead of free movements to the mainland.
From there, it’s trying a defensive game in the west, while pushing the resources you need in the east!