Account history vs transaction

[BenjaminMichaelis]

This is a two part question that may or may not be related.

1. I imported a bunch of transactions from csv (worked great btw, only nit is automatically removing commas for you from the amounts column would be nice instead of having to run a script or do something else first). However, I noticed that the account history graph seems to be driven by the transactions, but the account balance was driven by the "History". This really confused me; what is the difference between history and transactions? Aren't these the same (transactions make up an accounts history)? I would expect that if I import transactions, those would drive the account balance, and all I may have to do is add a reconciliation transaction at the beginning or end to get the balance right.
2. I clicked the sync button on an account out of curiosity as to what it did (hoped it magically make transactions part of history but maybe still that isn't how it works) and it just showed this message and returned a 200 status code. ( I also logged out and in again since I saw that there is an issue about how a sync triggers at login, but I assume it's a different sync; however, worth a shot )
   

Just want to understand better! :)