U.K. Prime Minister Keir Starmer has made public what has been known privately for a while now: The United Kingdom will deploy troops as part of a non-NATO peacekeeping force designed to preserve any U.S.-negotiated end to the war in Ukraine. His announcement is welcome but carries numerous complications.

First, there is glaring opposition from Russia. Meeting with Secretary of State Marco Rubio in Saudi Arabia on Tuesday, Russian foreign minister Sergey Lavrov said any deployment of Western troops to Ukraine would be “completely unacceptable.” As the Washington Examiner has written in the past, this Russian opposition to Western peacekeepers underlines why President Donald Trump will have to stare down Russian President Vladimir Putin if he is to secure a meaningful peace accord on Ukraine.