"breakthrough"

I came across the following passage the other day:

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Many attempts were made to reform the situation, expand higher education, and introduce practical subjects into the curriculum, but they all came up against entrenched conservative forces. The breakthough came in 1826 when a University College was founded in London with a charter to award...
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"Breakthough"?

This is in the original passage, so usually, when citing, I should put [sic] right after "breakthough," indicating that the part is "incorrectly written."

In this case, the problem is a spelling error, which should have been "breakthrough."
"Through" has such a tricky spelling indeed that it sometimes ruins the efforts of writer's revision. There are some words with the close spelling: though, thorough, tough, throw. . .

According to "Hellog" website, "through" in late Middle English has as many as 515 different ways in spelling. You can see all the spellings in the following page:

http://user.keio.ac.jp/~rhotta/hellog/2009-06-20-1.html

It's simply amazing how people of the time were able to recognise the word form and its meaning. Apparently, the multiple spelling from is based on each scribe's habit of writing.

The diverse nature of English spelling in the Middle Ages far surpasses our modern expectation and conception!