Greenland has become the island that could break NATO

European leaders have sounded the alarm over Donald Trump's ambitions to take over Greenland, but the U.S. president may instead be thinking of his legacy. If that's the case, many analysts, diplomats and politicians believe not only will European diplomacy fail, but the entire post-Second World War system of alliances will come crashing down alongside it, should the U.S. move unilaterally.