Germany's would-be next chancellor, Friedrich Merz, won lawmakers' approval to loosen strict debt rules for higher defense spending as doubts mount about the strength of the trans-Atlantic alliance.

Germany's parliament approved plans for a massive spending surge on Tuesday, throwing off decades of fiscal conservatism in hopes of reviving economic growth and scaling up military spending for a new era of European collective defence.

Germany's lower house of parliament is set to vote on Tuesday on a massive surge in borrowing that could boost Europe's largest economy and stimulate growth across the region, even as it faces trade tensions with top partner the United States.