Complex sentence: In November 1944, he went into disagreement with Aris Velouchiotis, who wanted ELAS to prepare to fight the British and during the December fighting, the Macedonian wing of the ELAS didn't fight against the British troops.
Split into simpler sentences: In November 1944, he went into disagreement with Aris Velouchiotis, who wanted ELAS to prepare to fight the British. During the December fighting, the Macedonian wing of the ELAS didn't fight against the British troops.