At the beginning there were more on the German side but when the US entered the are it evened out. There are no exact numbers though.
The US did not belong to any side at the beginning of WW1.
Both sides used aircraft, early in the war, as reconnaissance. When the war started each side had a small number of aircraft on hand, so they were used almost from the beginning.
Each side made there own.
entente and central powers
September 1, 1939 was the official beginning of World War 2.
Attrition.
America's population at the beginning of world war 1 was considered mobilization. After World War One fifth of the world's population was infected.
victory and more land
At the beginning of WWII, America was neutral. The US did not enter the war until 1941, after the attack on Pearl Harbor.
In 1917 the Lusitania - a ship - was sunk with Americans on board.
There were many countries that were controlled by Great Britain at the beginning of World War 1.