Complex sentence: Chandernagore, which was earlier part of French India, had voted to join India in a plebiscite in 1949 and formally joined India in 1952, finally becoming a part of the Hooghly district of West Bengal on 2 October 1954.
Split into simpler sentences: Chandernagore, which was earlier part of French India, had voted to join India in a plebiscite in 1949. Formally, it joined India in 1952 and finally became a part of the Hooghly district of West Bengal on 2 October 1954.