I'm glad you took the time to respond, so to make this easier to understand, provide some context and to get a clear picture.
Simba: Before the removement of the pervious government, the country was a Monarchy. Now a military junta, with a marshal who declared himself as "Emperor of the Pantheras", by his own words, "The will of the Panthera." He and his regime wants to create a unified ethnostate. This of course followed imprisonment, killings, and kidnappings of political opponents.
The Federation: A political union of states. One of the poorest, politically corrupt country until a period of steady economic development later in the decade. No exception to the first, its government is under a one-party state.
To provide more context, this has been simmering for several years between the two, with many disagreements; however, the circumstances surrounding such aren't clear, only to say that if it wasn't along ideological or racial differences, the border was to blame. Incidents, clashes, incursions, and funding of groups opposing both sides had been the norm since the late 60s and continued into the 70s. If it hadn't been for intervention from higher powers and diplomacy from an unspecified neighbor from the east, things could've gotten hot in ‘72 for an unsuccessful coup and an attempted assassination on Simba's leader. A truce was reached, and fighting ceased, but tensions remained high. Six years later, as retaliation, they embracing irregular warfare, the formation of commandos trained to infiltrate the country, hoping to incite the anthros in the south-eastern regions to an insurgency. And others, bombing infrastructure, targeted VIPs, and so on. Now, the famous "State House Raid" was an attempt by Simba's specialized unit to either kill President on his birthday, a more symbolic operation to ensure political turmoil and a call to rise up, but it failed. The following day, war was declared. To add, yes there were other countries involved on both sides.