You want my answer? none. why? because it costs a SIGNIFICANT amount of money, manpower, and equipment to transport that many soldiers to retain a control of USA. Yes the country will control USA but TEMPORARILY. The history has shown this many times.
2 major reasons why seizing USA will be an
epic fail:
1. geographical advantage
2. Amendment 2
To answer your question, Jolie...
India? absolutely not. While they have huge numbers of manpower... they lack mindset and especially military infrastructure to seize America. They cannot seize USA without getting seized by Pakistan. Beside India's our friend.
Russia? nope they're not interested at all. They have their own problem to deal with the former USSR countries especially Georgia, Chechnya, Afghanistan, etc... They will attack Russia if Russia sent a significant portion of its military resource on USA.
England? no they're our friend. they will most likely have their own internal problem financially and politically if USA collapses...
Middle East? extraordinary unlikely since their military infrastructure is LAUGHABLE. They don't even have aircraft carrier! How are they going to transport their troops & equipment to USA? Beside - Israel will pound on their ass.
China? Possible but in the end - it will be an epic fail. Most likely scenario to transport significant amount of troops and equipments across the ocean - by using hundred of oil tankers and cargo ships. They will hit the West Coast hard and we will lose 1/4th of USA.
Despite of invasion.... no nuclear war will occur. When you say "USA collapses"..... that means the federal government (White House & D.C.) has collapsed. There is no chain in command. However... the beauty of USA that NO other country has is.....USA has a capability to function as decentralized government... meaning there are 50 states acting independently with their own leaders (Senators/Governor), national guards and citizens. it will no longer be called as United States of America but it'd be simply called as "America". Each state has their own name and flag. Chance is - several states will band together... forming a faction.
It is highly likely that there will be 2-3 factions. The most powerful one will be.... you guess it! Texas! and another faction will most likely be Ohio. Texas has OIL, military, and lands (crops) so this faction will consist of mostly mid-western states while Ohio will control most of Eastern coast. Texas faction will most likely have air & marines superiority while Ohio faction will most likely have naval & army superiority.
The reason why I say it will be an epic fail to seize America is because it is impossible to completely seize USA. Many examples we have seen in history when a nation tried to control numbers of countries -
Hitler - failed
USSR - failed
Roman Empire - failed
Japanese Occupation - failed
British Empire - failed
many more....
God Bless America! that's how much faith I have in America