“after his 20-year prison sentence was upheld”
For crimes in the 1990s. So he didn’t get “time served” and released?
He wanted a mostly-Croat part of Herzegovina to be independent of the Muslim Bosniaks. That area had been assigned to Croatia in 1939 in the "Sporazum" setting up an autonomous Croatia inside the Kingdom of Yugoslavia, and Tudjman apparently hoped to annex it, but as far as I can tell the average citizen of Croatia is not interested in annexing any part of Bosnia.
Praljak seems to have been responsible for the destruction of the old bridge in Mostar (later rebuilt).