Confused by the grammar

The sentence that confuses me:

It has taken so long for historians to focus on the civil law of early modern England.

At first, I thought it means that historians have been focused on the civil law for a excessive long period. After checking the translation in my first language, I was surprised that it actually means that there is an excessive long period before the historians start to focus on the civil law. That’s quite counter-intuitive to me. Could anyone explain the mechanism behind this? Also, how will you say in English my wrong perception?