English problem - grammar question?

I am writing an essay, and i have some confusion about tenses.

If i write something about the past in my essay, but in some parts of the essay, I'm writing something which is my personal statement or opinon about it, or something that is still true to this date, do i write them in past tense or present tense?

example:
The Europeans were...... Because of this, it determines
or it distinguishes
it symbolises

(Should these be written in past tense, present or either? i.e.
should it be be written as "determines" or "determined" or either?)

Thank you.