How did English become lingua franco of so many countries?

The British began establishing colonies and trading posts in many places in the world in the 16th through the 18th centuries. These developed to form the British Empire which lasted until a few decades ago. English became the imperial language in most parts of the empire. Just as the British Empire was fading the United States arose as a new centre of enormous power in the world with many trade and military bases around the world all speaking English to this day.