Yeah, when did the French jump in? After Saratoga when it was almost definite we wouldn't be conquered.
Oh geez ... are we really going to have this discussion?
First, history lessons. The war began in 1776. Saratoga was Oct, '77. The French came in Feb, '78. Cornwalis was defeated in Oct, '81. The Battle of Saratoga DID NOT guarantee American victory in the Revolutionary War but it did prove that an American force could win a battle against the British.
Second, the US didn't enter WWI until 1917 when there was only about a year left in the war.
We entered WW1 in time to stop the Last German offensive. You know, the one where they almost took Paris even with us there. So we kinda saved their butts by getting involved.
The French got into the Rev War after they knew we wouldn't be crushed. We won at Saratoga and proved that the british weren't going to crush us.