B-5 question

I never watched Babylon 5 when it aired on TV,but have a friend who has given me all 5 seasons on DVD. The one thing I still can't figure out is; What was the importance of Babylon 4 going back in time other than getting Sinclair back in time and doing the crystallis thing? B4 had no defenses and Sinclair was the only one on board so how did sending it back turn the battle around?

Anyway it was a very good series that I can appreciate now that I have time to relax and watch TV.

They needed a base to launch there attacks from. At that time they didn't have the long range ships. Kind of like having to take Guadalcanal.

Alright,it just seemed as though they were in a battle and B4 showed up and all was well. That makes more sense.
I finished season 5 last night and I must say the last few episodes really were depressing (That may not be the word I was looking for,maybe sad would be better). Now I'm off to find the movies or Crusade.

I have the crusade episodes and it could have been a great series. Its sad it only lasted one series.