WASHINGTON (Reuters) - The rules-based order of multilateralism is increasingly under threat and leaders must uphold international cooperation, German Finance Minister Olaf Scholz said in Washington on Friday, calling on the United States to overcome trade differences with Europe.U.S. President Donald Trump's threat this week to impose tariffs on $11 billion (£8.4 billion) worth of European Union products, including commercial aircraft, has opened a new front in his global trade war and..