Complex sentence: After the initial British landing in Mersin, on 17 December 1918, the whole of Çukurova was occupied by the British troops; from 1 January 1919, they were replaced by French troops.
Split into simpler sentences: After the initial British landing in Mersin, on 17 December 1918, whole Çukurova was occupied by the British troops. However, beginning by 1 January 1919, they were replaced by the French troops.