Complex sentence: The Quebec Agreement established a new Combined Policy Committee to direct the joint project, but the Americans disliked Akers, and so Chadwick was appointed technical advisor to the Combined Policy Committee, and the head of the British Mission.
Split into simpler sentences: The Quebec Agreement established a new Combined Policy Committee to direct the joint project. The Americans disliked Akers, so Chadwick was appointed technical advisor to the Combined Policy Committee, and the head of the British Mission.