Bosnia is home to three main ethnic groups. The Bosniaks, who are mostly Muslim, the Serbs who are mostly orthodox Christian and the Croats—they're mostly Catholic. And don't get confused with Serbians or Croatians, which is what people from Serbia and Croatia are called, although they share history, tradition and religion with the Serbs and Croats. Now, Bosnia's ethnic divisions were a big part of the war that happened in the 1990s. After Yugoslavia broke up, there was a power vacuum and all those ethnic groups started fighting each other for territory. In 1992, the UN recognised Bosnia and Herzegovina's independence, and that didn't go down well with Serbs. Various Serb forces attacked, and that was the start of the Bosnian war. Fighting went on for three-and-a-half years. Atrocities were committed by all sides. Roughly 100,000 people were killed, about 80% were Bosniaks. In the town of Srebrenica, Serb forces killed more than 8,000 Bosnian Muslims—men and boys. A UN tribunal later called it a genocide. The war ended in 1995, with the Dayton Peace Agreement, a deal brokered by the US. Europe and Russia were also involved. It included a new constitution for Bosnia that tried to balance political power between the Bosniaks, Serbs and Croats. But in many ways, that constitution only reinforced those ethnic divisions. So keep that in mind while we tell you what the system looks like. There's the state level that deals with the whole country, but instead of one president at the top, they have what's called a tripartite presidency. It means three people share the presidency, and it's always one Bosniak, one Croat and one Serb. There's also a prime minister and a parliament at the state level. And this is where things like foreign policy and the army are dealt with. At the next level down, you've got two self-governing entities. There's Republika Srpska and the Federation of Bosnia and Herzegovina. And don't confuse the federation with the name of the country. And there are more layers of government below those, but there's another layer we need to talk about. And that's back at the top—the high representative. The high representative is never a Bosnian. They're usually from the EU. The current one's German. So, in some ways, you can think of Bosnia as a kind of protectorate. It really depends on the international community, especially the US and EU, to keep the peace. The whole system is completely rooted in the Dayton agreement. But right now, that system is looking a bit shaky. A lot of that has to do with this man, Milorad Dodik. He's the Serb member of the tripartite presidency. And that rhetoric has risen in the last few months. Dodik threatened to pull out Republika Srpska from the main state-level institutions—the judiciary, the tax authority and the army—and set up separate Serb ones. Serb politicians have also been refusing to participate in many state-level institutions. It's paralysing the system and nothing's really getting done. And then in Republika Srpska they went ahead with celebrations to mark what they call their National Day, which Bosnia's top court has ruled illegal. Now, there are a couple reasons why things have heated up so much lately. Last July, the high representative at the time—remember that's the top foreign official we talked about earlier—he brought in a new law to make genocide denial a crime. It's something that Bosniaks, in particular, have been calling for for a while. The law doesn't single out any ethnic group, but many Serbs feel the law unfairly targets them, and Dodik and his allies have pushed this idea, too. There's another big thing going on that Dodik is unhappy about. It's a long-running dispute over public agricultural land within Republika Srpska. Dodik insists it belongs to Republika Srpska, but Bosnia's Constitutional Court declared it belongs to the state. So Dodik wants that decision overturned, and he's using it as a bargaining chip. Now there's another dimension to all of this: elections, which are in October. It means a lot of politicians are riled up, including Dodik. So that paints the picture of what's going on inside Bosnia. But what about the role of the US, the EU and NATO in all of this? They're the guarantors of the Dayton agreement. The US imposed new sanctions on Dodik for what they called "significant corruption and destabilising activities". And the EU has a small peacekeeping force in Bosnia, currently around 600 soldiers. But some people think that's just not nearly enough, and is one of the reasons things have gone this far. The big shadow over this whole crisis is the fear that it could escalate into another conflict. And Bosnians are all too familiar with the worst-case scenario. So even though some people say Dodik isn't serious about following through with secession, just by raising it he also raises the stakes. If you found that useful, check out our recent explainer on what's happening in Ukraine. And if you have other ideas for news stories you want explained, let us know in the comments. See you next week.