Complex sentence: French contacts with Burma, effectively a British colony, would become almost non-existent, while from the second half of the 19th century France would concentrate in the establishment of French Indochina and the conflicts with China leading to the Sino-French War.
Split into simpler sentences: French contacts with Burma, effectively a British colony, became almost non-existent. Instead, from the second half of the 19th century, France concentrated on the establishment of French Indochina and the conflicts with China leading to the Sino-French War.