Why does Serbia object Kosovo wanting Independence?

Why are they rioting and objecting Kosovo's independence?

Also, what was Kosovo before it gained independence? Who there declared it? Thanks!!!

They believe that Kosovo is what defines Serbia. It is their land and nobody can take it away. Kosovo is not a city or county, it is the region, so they had their own government. And after the 1999 war, they got a president as well as a prime minister. So those people declared its independence. Over 90% of people in Kosovo are Muslims, so in 1999 Serbs, who are Orthodox, were fighting them and mass killed over 10,000 people, as well as raped women, beat them, and made them leave their homes.
This is a very smart move by Kosovo. They realize that other than Russia nobody likes Serbia or can work with them. And they believe, which I also believe, that Serbian people will lose their state, so Kosovo made a move to save itself, screw rest of Serbia for being clueless. And the problem is that Kosovo is and has always been part of Serbia, and losing that region will hurt them and move them closer to extinsion of their state. Their economy is doing bad, and as I stated already other countries don't like to or want to work with them or help them, and as much as Russia wants, they too are suffering and need food. So Russia likes to talk and make threats, but US, Britain, France, and Germany just avoid them because it is meaningless to wasre time listening to them. And all you have to do is give Russians a loaf of bread and they will play by your rules.
After the war, they tried to save the name Yugloslavia and lost it. Then they tried to expand with Serbia and Monte N3gr0 unity and then MN moved on because it was impossible to work with Serbia. Now Kosovo breaks away, they don't have much left, and this is actually why they are soo upset, and Serbian governmeent, military, and police all support them and encourage people to protest and riot. They see that this brings them that much closer to losing their nation-state and its millions of people not having a state.

because they've live there long before Albanians came