President Donald Trump has undermined the international system the U.S. built post-WWII. His actions include siding with Russia in the Ukraine war, threatening allies, and questioning NATO commitments ...

After the fall of the Soviet Union, Ukraine inherited a significant nuclear stockpile. Despite having these nuclear weapons, Ukraine relinquished them due to financial burdens and geopolitical risks.

His actions suggest he is most comfortable in the 19th-century world of great-power politics, where he, President Vladimir V. Putin of Russia and President Xi Jinping of China negotiate among ...