Complex sentence: Napoleon's troops, under the command of his brother-in-law, General Charles Emmanuel Leclerc, were to seize control of the island by diplomatic means, proclaiming peaceful intentions, and keeping secret his orders to deport all black officers.
Split into simpler sentences: Napoleon's troops, under the command of his brother-in-law, General Charles Emmanuel Leclerc, planned to seize control of the island by diplomatic means. They proclaimed peaceful intentions, and kept secret his orders to deport all black officers.