Complex sentence: The Dutch were the permanent friends and protectors of Cochin, but they withdrew their contingents from the field when the Zamorin promised to give back to them'Chetwai' which he had conquered from them on his way to Cochin.
Split into simpler sentences: The Dutch were the permanent friends and protectors of Cochin. But they withdrew their contingents from the field when the Zamorin promised to give back to them'Chetwai' which he had conquered from them on his way to Cochin.