Relativity makes interstellar war horribly unbalanced.  The further (and faster) you travel, the more outdated your weapons, armament, and tactics will be compared to the enemy.  Even if it takes you only a month subjectively of travel at 90% the speed of light to get to the front, several hundred years might have passed since you embarked.  What will the enemy be like by then?  Will that location even be a hot zone by the time you arrive?

Furthermore, will you recognize home if you ever return to it?

This is the basis for the award winning novel The Forever War by Joe Haldeman.  The story follows William Mandella, a physics grad conscripted into the war against the enigmatic Taurans.  Stuck in a war he doesn't want to fight, for a world getting more and more alien to the one he remembers, William does his best to cope and survive.  As a veteran himself, the author does a fantastic job of conveying the feeling of displacement.  Whether that feeling comes from being promoted beyond a soldier's comfort, or returning home to be at best a curiosity and at worst a target for anger.

Since this novel was written in the 70's, you have to relax judgement of the initial time scale.  Considering mankind had recently gotten to the moon, and the remarkable technological advances of the 20th century, it seemed reasonable to predict we'd be landing people on Charon (largest satellite of Pluto) by 2007.  Obviously this has not happened.  But once the first jump to another system occurs, the story moves forward enough in time that it won't bother you.

This book often finds itself in the top ten science fiction novels of all time, and with due reason.  It's not just about aliens, space battles, and the effects of time travel.  It's about humanity.  As long as humanity continues to change technologically or sociologically, this story will continue to be relevant.  As every person ages, they undoubtedly experience cases where society has changed "for the worst".  Whether that be newfangled contraptions or clothing you never would've been caught dead in.  It's that sense of being out of touch that this book zeroes in on with deadly accuracy.

The Good: Well paced. Believable characters. Left me wanting more, even though there was no more story to tell, and it had already spanned over a dozen centuries.
The Bad: I don't understand "collapsars" or their explanation.  You're safe to consider it technobabble anyway, and doesn't detract from the story.
The Ugly: Humanity's method of population control.  I suppose at that technology level anything is possible.

Ha!  Great minds and all.  I just got that book for Christmas and finished it in two days.

I liked how after his first tour Mandella finds earth so different as to be alien to him.  I experienced that, though to a much smaller degree, when I came home from Japan.

I agree with your Ugly point, that population control method really doesn't hold up to the logic test at all!

Quoted from Hawkeye

I agree with your Ugly point, that population control method really doesn't hold up to the logic test at all!

One possibility is they added something to the water supply, so that everyone was effected.  Much more reliable than expecting people to be responsible.