▁an ▁important ▁political ▁victory ▁in ▁se cur ing ▁the ▁control ▁of ▁the ▁Mal u ku ▁Islands , ▁the ▁" Sp ice ▁Islands " ▁claimed ▁by ▁Spain ▁since ▁the ▁Mag ellan - El cano ▁circ umn avigation . ▁After ▁almost ▁a ▁de cade ▁of ▁sk irm ishes ▁in ▁S out heast ▁Asia , ▁he ▁signed ▁the ▁Tre aty ▁of ▁Zar ago za ▁with ▁Emperor ▁Charles ▁V ▁on ▁ 2 2 ▁April ▁ 1 5 2 9 . ▁It ▁defined ▁the ▁areas ▁of ▁Spanish ▁and ▁Portuguese ▁influence ▁in ▁Asia ▁and ▁established ▁the ▁anti - mer id ian ▁to ▁the ▁Tre aty ▁of ▁T ord es illas . ▁ ▁International ▁relations ▁The ▁reign ▁of ▁John ▁III ▁was ▁marked ▁by ▁active ▁diplom acy . ▁With ▁Spain , ▁he ▁made ▁al li ances ▁through ▁marriage ▁that ▁ens ured ▁peace ▁in ▁the ▁I ber ian ▁Pen ins ula ▁for ▁a ▁number ▁of ▁years . ▁He ▁himself ▁married ▁Catherine ▁of ▁Austria , ▁the ▁daughter ▁of ▁Philip ▁I ▁of ▁Cast ile . ▁His ▁sister ▁Isabel la ▁of ▁Portugal ▁married ▁Charles ▁V , ▁the ▁king ▁of ▁Spain ▁and ▁Holy ▁Roman ▁Emperor . ▁His ▁daughter ▁Maria ▁Man uela ▁married ▁King ▁Philip ▁II ▁of ▁Spain ▁– ▁and ▁there ▁were ▁others . ▁However , ▁the ▁inter mar riage ▁of ▁these ▁closely ▁related ▁royal ▁families ▁may ▁have ▁been ▁one ▁of ▁the ▁factors ▁that ▁contributed ▁to ▁the ▁poor ▁health ▁of ▁John ' s ▁children ▁and ▁of ▁future ▁King ▁Sebastian ▁of ▁Portugal . ▁ ▁John ▁III ▁remained ▁neutral ▁during ▁the ▁war ▁between ▁France ▁and ▁Spain ▁but ▁stood ▁firm