It all began when the Angles, Saxons, and Jutes took over the Celtics in the British Isles.
When the Normans invaded The British Isles, French words were incorporated into Old English, the Anglo-Saxons' language.
French was associated with higher class, while the peasants' English was associated with lower class. The peasants tried to incorporate French words to sound sophisticated.
English continued to diffuse, as the British colonized and built America, and the U.S. then spread the language to other places like the Philippines.
Using English to communicate is very common now since many countries were British colonies. So, often, companies that don't speak a partner's language will use English as a common language.
Hello, it's very nice to meet you. so today we will be discussing the new trading agreement ...
Oh, what? You said Franca? huh, like your name!
Now, English is being used even when it's not for trade/communication. A lot of countries, like Korea use English in songs and everyday life. Taiwan is even making English an official language. Now that's the story of how English became a Lingua Franca.