Answer: The winning of the war in Europe against Germany.
This was the "Europe first" strategy, coupled with simply holding Japan at bay in the Pacific theater of the war until Germany was defeated. With the scale of the war and the resources needed to defeat the powerful Axis powers, there was a challenge to allocate military personnel and hardware. The strategy was to win the war in Europe first, and then go after Japan.
D. England
All of the other three were actively competing for Korea at the time along with America as well.
The main source of conflict at the Constitutional Convention was in regards to federal v. state power.
Federalists v. Anti-Federalists fought for weeks through published essays to push forward their view on whether their should be a strong Federal government or whether there should be a weak federal government to allow for strong and sovereign states.