I will analyze the major differences between 1939 and 1944 here.
1. Nukes:
Moscow and several American Cities can build Nukes
2. Super Tanks:
Many Major cities can build them
3. Country Changes:
China has 3 stars
Germany has 1 star
US controls Northwest Spain and Belgium
Russia controls Poland, Romania, and Yugoslavia
Japan controls French Indochina/Vietnam/Hanoi
Britain controls Denmark, Libya, and Rome
Germany controls the Netherlands and Bulgaria
Patton and Bradley are in Europe
Mitscher with Carriers and Battleships replaces Donitz's Submarines
Koga replaces Yamamoto
Japanese Submarines near Philippines are replaced by US forces
Most Russian spawns are on the map at game start
Most German spawns spawn in the first few turns
4. Reward:
400 for 3*
800 for 2*
1200 for 1*