Original:  To its south and east, Chile used military force and colonization to occupy Araucana , a still undefeated indigenous nation (1861-1883) and although Chile retained westernmost Patagonia and the Strait of Magellan with the treaty of 1881, it yielded to Argentina most of Patagonia and its access to the Atlantic to avoid the outbreak of war in multiple fronts during the War of the Pacific .
Revised:  To its south and east, Chile used military force and colonization to occupy Araucana , a still undefeated indigenous nation (1861-1883) and successfully dispute Argentine claims over westernmost Patagonia and the Strait of Magellan with the treaty of 1881, it yielded to Argentina most of Patagonia and its access to the Atlantic to avoid the outbreak of war in multiple fronts during the War of the Pacific .
Edit intent: meaning-changed