Learn English – Why did “insofar” become a word, not “insofaras”

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.

Expanding on Janus's excellent suggestion (make the search string more context-specific), the "switchover point is much clearer if you graph deaths from consumption/tuberculosis...

So we can reasonably say tuberculosis was already gaining currency before WW1, but by the end of the war it had almost completely displaced consumption. Perhaps because when a major protracted war ends, people want to make a fresh start in terms of language as well as politics and society.

My guess is that the actual cause of the disease (infection by tubercle bacillus) wasn't generally recognised until the turn of the century. The "germ theory" of disease is much associated with Louis Pasteur, 1822 - 1895, but as it says in that link...

During Louis Pasteur's lifetime it was not easy for him to convince others of his ideas, controversial in their time but considered absolutely correct today.