around 1531, a plan emerged to wed isabella to john zápolya, voivode of transylvania and king of hungary. when louis ii of hungary was killed in the battle of mohács in 1526, hungary was divided between pro-habsburg royal hungary and pro-zápolya eastern hungarian kingdom. the parties were engaged in the little war in hungary. zápolya had sustained his claim only by gaining support from and becoming vassal of the ottoman empire. bona sforza, ardent opponent of the habsburgs, supported zápolya and tried to convince her husband sigismund to provide military support and isabella's hand. sigismund, whose first wife was zápolya's sister barbara, refused, not wanting to upset the habsburgs and doubting zápolya's ability to hold onto his throne. eventually, sigismund relented on a condition that a peace treaty was concluded between zápolya and the habsburgs. the treaty of nagyvárad was signed in february 1538 in part due to sigismund's requirement. archduke ferdinand of austria and zápolya agreed to divide hungary between themselves and that ferdinand was to inherit zápolya's territory since at that time he was childless.