history - Why did English become a universal language and when?

As we all know, English is the universal communication medium. Now we know how powerful it is to convey our thoughts. When did it become a common language? Why did they opt for this language?

Answer

English became the lingua franca around WWII, but it was already used all through the British Colonial Empire, establishing it in North America and Australia among others. here is a citation of Wikipedia:

It[English] has
replaced French as the lingua franca
of diplomacy since World War II. The
rise of English in diplomacy began in
1919, in the aftermath of World War I,
when the Treaty of Versailles was
written in English as well as in
French, the dominant language used in

diplomacy until that time. The
widespread use of English was further
advanced by the prominent
international role played by
English-speaking nations (the United
States and the Commonwealth of
Nations) in the aftermath of World War
II, particularly in the establishment
and organization of the United
Nations.
[...]
When the United Kingdom

became a colonial power, English
served as the lingua franca of the
colonies of the British Empire. In the
post-colonial period, some of the
newly created nations which had
multiple indigenous languages opted
to continue using English as the
lingua franca to avoid the political
difficulties inherent in promoting any
one indigenous language above the

others. The British Empire established
the use of English in regions around
the world such as North America,
India, Africa, Australia and New
Zealand, so that by the late 19th
century its reach was truly global,
and in the latter half of the 20th
century, widespread international use
of English was much reinforced by the
global economic, financial,

scientific, military, and cultural
pre-eminence of the English-speaking
countries and especially the U.S.
Today, more than half of all
scientific journals are published in
English, while in France, almost one
third of all natural science research
appears in English, lending some
support to English being the lingua
franca of science and technology.

English is also the lingua franca of
international Air Traffic Control
communications.