Following the first Balkan War, Serbia and Montenegro expel their Bosniak populations to Austrian Bosnia. Today that means about ~250,000 more Bosniaks in Bosnia[1].
In the 1990s, Bosnia negotiates with Croatia to establish a southern boundary along Dalmatia in which majority Croat areas are ceded to Croatia. Without having to fight Croatia, the Bosniaks direct all their attention towards the Serbs, resulting in Bosnia being less devastated and fewer Bosniaks emigrating.
After WWII, the communist opt not to take revenge on the Germans of Vojvodina, seeing them as otherwise separate from the Nazis.
The result of the Kosovo intervention meanwhile is turning Serbia into the Serbian Federal Republic of Serbia, Montenegro, Vojvodina, and Kosovo.
Bosnia is 3.4 million people in 2019 TTL, ~70% Bosniak, and a unitary state.
Serbia is 10 million people in 2018 TTL and 62% Serb, 19% Albanian, 5.8% Romani, 4% German, 3% Montenegrin, 3% Hungarian, 0.6% Croat, 0.3% Macedonian, etc.
[1] Today there are 145,000 Bosniaks in Serbia, 55,000 in Montenegro, 28,000 in Kosovo, and 17,000 in Macedonia, aka the countries that in 1913 would comprise Serbia and Montenegro.