When the U.S. Army Expeditionaray Force arrived in France in 1918,
the British and French high command intended to break it up,
and use the American battalions to fill up existing French and British divisions.
John Pershing, the U.S. commander refused to cooperate with that plan.
He wanted his units to fight as a coherent army.
The high command largely ignored him,
and he actually threatened to pack up his army and take it back home.
He meant it.
They believed it.
And the U.S. forces fought as a whole.