Two months ago, when President Trump was threatening to annex Greenland, I spoke with Danish and other European officials who warned of lasting damage to the system of alliances that the United States created after the Second World War, above all NATO. At the time, this seemed like a theoretical proposition. Denmark and other allies had come to the aid of the United States after the September 11 attacks, sending soldiers to fight in the American-led war in Afghanistan; these same countries, officials and experts hypothesized, might be less inclined to help in the future. But the possibility that the United States would actually require European assistance, especially in the Middle East, appeared faint. After all, Trump had promised to curtail military adventures, in order to refocus on American interests in the Western Hemisphere. The decision to wage war against Iran changed all that. Despite his earlier claims that the American military had already vanquished Iran and didn’t need partners to join the fight, Trump is now actively soliciting the help of other countries to …