Complex sentence: Armenian borrowed so many words from Iranian languages, for example, that it was at first considered a branch of the Indo-Iranian languages, and was not recognized as an independent branch of the Indo-European languages for many decades.
Split into simpler sentences: Armenian borrowed so many words from Iranian languages, for example, that it was at first considered a branch of the Indo-Iranian languages. It was not recognized as an independent branch of the Indo-European languages for many decades.