Secretary of State John Kerry on Tuesday saluted German Chancellor Angela Merkel for welcoming thousands of refugees into her country, and warned against “demagogues” who would undermine the alliances that have formed in the decades since World War II.

“To some, formulating the right response to refugees is as easy as putting up a green light or a red one; they just think it’s simple,” Kerry said during a speech in Brussels on Tuesday morning. “Chancellor Merkel and other European leaders should be commended for trying to cope with this crisis in a humane way that is respectful of the lessons of history.”