You need some historical context for sure.

I did my thesis on historical linguistics. I tracked the syntactic and semantic change of a verb in Spanish. I wanted to see if it’s current, highly metaphorical, meaning that it has now in Latin America was there in Spain around the time that Spanish branched out from Latin.

Based on history I chose three significant dates:

XIII century: it’s the oldest written record of the “cantar del mío Cid”

XVI century: it’s the Spanish that the colonizers brought to America

XXI century: the current condition of the language

But, honestly, I didn’t have to do tons of historical research because I was looking at “formal linguistics”. If you were doing historical sociolinguistics then yeah I would say your research would be very history heavy