English has become a global language for a few different reasons. First, the British Empire visited, colonized, or began many of the populations over the world. Therefore, their language impacted more areas than any other language. English has also become a global language based upon necessity.
What is meant by this second reason is that the world is becoming more globalized. Businesses trade with other businesses all over the world. Scientists from all over the world meet to discuss important issues. People travel more. These reasons, while very limited, denote a reason for a global language to exist. It would seem that since the English language was already embedded in so many different ares that it would make sense to push for English to be the global language.
Outside of that, English has simply been readily accepted as a major global language. Schools all over the world are teaching it. Given that it has not undergone enough scrutiny, and has had no real opposition, people have accepted English as a global language.
When businessmen from Brazil and Germany do business with a supplier or customer in China, they speak English.
I think people all around the world speak English because the British Empire sent British ships around the world, even to non-British ports. In every port, British sailors played football and spoke English with the local people. In the process, football and English spread around the world.
Then the British sent the American GI's. Can you believe it? They also speak English. I know that George Bernard Shaw or was it Alan Jay Lerner insisted that Americans don't speak English, but what did they know?
I live in a neighborhood with people who met American GI's in Russia (Russian Revolution), Haiti (1920's), Mexico (looking for Poncho Villa, but around here we call him Frank), Britain, France, Italy, Algeria, and Germany (my great grandfather during World War II), Japan (After the Pacific War), Lebanon and Belgian Congo (1950's), Columbia (looking for Cocaine smugglers), Saudi Arabia (after the Gulf War, my town has three mosques), Iraq (after the Iraq War), Granada, Panama, Central America, Vietnam, Thailand, Philippine Islands, Haiti a second time, Pakistan, Burma, China, Afghanistan, etc.
Then came movies and television shows. Do people in Italy watch the Sopranos in English or Italian? My grandfather says that he watched American televison shows on Manila television stations in the 1960's.
With so many people, British and their American cousins, all around the world, one wonders how people could not speak English.