-To understand reasons for waging one of the most deadliest wars of 20th century we need to understand the chronology and the fact that we are not looking the conflict as one war, but as 4 different wars happening simultaneously . We need to know that all 7 different nationalities lived under one Communist regime. For almost 50 years Yugoslavian leadership successfully marginalized strong national awareness and extreme religious belief movement. This tragic combination set the spark for Balkan powder keg.
Ten-Day War
Slovenia Independence War was brief war that took place right after Slovenia declared independence on 25 June 1991. JNA (Yugoslav National Army) was defeated from a small Slovenian teritorial defense police with 66 casualties on both of the sides. Regime quickly withdrawed their army due to the fact that much bigger problems were comming around the corner.
If you want to know more about Ten day war go to : https://en.wikipedia.org/wiki/Ten-Day_War
Croatian War of Independence
City of Vukovar
Shortly after Slovenia, Croatia declared its independence too , starting a bloody Croat-JNA war. Yugoslav National Army was now controlled mostly by Serbs, and Yugoslavia technically ceased to exist. Serb people felt endangered, so shortly after Croatia's independence tensions erupted and new war started in Slavonia and Knin. It lasted from 1991 to 1995. For more information on war in Croatia please do check : https://en.wikipedia.org/wiki/Croatian_War_of_Independence 
War in Bosnia
Siege of Sarajevo
Bosnian- Croat War
War in Bosnia is actually separated in two different wars; Bosnian-Serb war and Bosnian-Croat war.
Bosnian-Serb war started in 1992 and it is remembered for the second largest genocide in Europe after Jewish Holocaust when over 8000 Bosnian's died in UN demilitarized zone in Srebrenica. It is also remembered for the longest siege in modern warfare. Siege of Sarajevo lasted from 1992 to 1995 and it was done by Bosnian Serbs who took the hills surrounding Sarajevo. Bosnian-Croat war erupted in 1993 in city of Mostar. Almost whole city was destroyed by people who lived in it, and climax of the war lasted through summer of 1993. Bosnia is now separated on Bosnian Federation and on Republic of Srpska
You can see more information on this link : https://en.wikipedia.org/wiki/Bosnian_War
I tried to make this post purely informative and educational , unbiased as much as I can be .War is the worst thing that can happen to human kind. Hope you liked it.