There are a couple of sentences:
The water froze and caused the pipe to burst.
If it is a succession of past events it should be Past Simple. But if the first part happened earlier, it should be : The water had frozen and caused the pipe to burst.So, can it be Past Perfect, or this sentence must be written in Past Simple?
Year by year the population of the West increased.
Should it be increased (Past Simple) or was increasing(Past Continuous) ? Because, I guess, Past Simple does not belong here .
I don't know which tense to choose. There is no extra context, just sentences on their own.