I've got a love for classic sci fi, not just reading the greats but finding previously unknown (to me works). I'm reading Gordon R Dickson's 'Dorsai' saga though it's more commonly referred to the Childe Cycle, there are several books and novels in the series. These are all set in the 21st century onwards where mankind has splintered into several sub groups following their departure from earth.
Tactics of Mistake
An interesting read of how an unproven military tactic, devised by a single man, can prove decisive in war.
Soldier Ask Not
Though published before ToM its set roughly 100 years after with common elements carried forward.
Just a side not it's important to me when getting these older books to find the editions with the time relevant artwork, modern versions are often ebooks with terrible covers!