Complex sentence: Eisenhower wished to take Smith and other key members of his AFHQ staff with him to his new assignment, but Prime Minister Winston Churchill wanted to retain Smith at AFHQ as Deputy Supreme Commander in the Mediterranean.
Split into simpler sentences: Eisenhower wished to take Smith and other key members of his AFHQ staff with him to his new assignment. However Prime Minister Winston Churchill proposed retaining Smith at AFHQ as Deputy Supreme Commander in the Mediterranean.