Martti Ahtisaari, a dogged Finnish statesman whose many quests to end conflict took him from the deserts of Namibia to secret arms caches in remote Irish farmlands, earning him the Nobel Peace Prize, died on Monday in Helsinki. He was 86. A foundation he created for preventing and resolving violent conflicts announced his death. He had been diagnosed with advanced Alzheimer’s disease, the Finnish president’s office said in 2021. In a statement on Monday, President Sauli Niinistö of Finland said Ahtisaari had “worked tirelessly to secure peace and life. Even for those who lived far away and in very different...