The League War was an event immediately following the the end of the Third Formic War.
Less than twenty-four hours after the xenocide of the Formics, tensions on Earth began to increase, mainly between the United States of America and the countries of the Second Warsaw Pact. America instigated that the Warsaw Pact was going to attack, while Russia accused the Hegemony of the same thing. Soon after, the war began.
The war was fought by various countries in order to seize control of the International Fleet and Ender's Jeesh, but primarily Ender Wiggin himself. America and the Hegemony sought to have him to command their armies, while the Second Warsaw Pact wanted him dead.
Ender and his Jeesh were currently on Eros, where the Russian Polemarch and marines of the same nationality also happened to be located. In order to protect him and the others, Hyrum Graff and other International Fleet personnel posted a guard outside Ender's door.
At some point during the war, the Strategos declared that Ender was loyal to the I.F., which led many on the side of the Warsaw Pact to change sides. Some of the Polemarch's soldiers turned on him when he ordered that they were to find and kill Ender.