It doesn't explicitly say anywhere that they ended that exact year. However, Mr. Zahn did state that he asked Lucasfilm about it when he was first outlining the Thrawn books, and was told that the Clone Wars had taken place 35 years before the first movie. Given that the Empire did not form until around the time of Luke's birth (about 15 years after this), the conclusion that the wars did not directly lead into the Emperor's takeover is obvious. He must therefore have used the chaos and destruction they left in their wake to gradually create a politically advantageous situation for himself.

Since the 'official' version of what happened in the Clone Wars is so outright terrible, it is frustrating that Mr. Zahn was not able to go into too much detail about the scenario he'd come up with. The tantalizing hints he was able to include are most intriguing, and point to a far more interesting story than what we actually ended up getting.