What did it take so long for US troops to entercombat

Reason as it took so long for US troops to enter-combat:

General Pershing sent the soldiers to the east of France for further training. This took so much time for American troops to fight as General Pershing sent soldiers for training in eastern France for further preparation to be able to combine with British and French soldiers with a very large German army of 260 divisions.

In compliance with the petition of the UK and France, as a result of a powerful German offensive, the President decides that, should the need arise; the American forces should combine with the French and British armies, as little as the companies around the world. The solution comes in the form of an agreement signed in Dec, 1917.