Barack Obama issued a stark warning against growing nationalism in America and throughout the world at the Economic Club of Chicago, invoking complacency and the rise of Nazi leader Adolf Hitler.

Former President Obama told the forum’s audience on Tuesday at a question and answer session that the danger at hand was “grow complacent,” according to ChicagoBusiness.com.

“We have to tend to this garden of democracy or else things could fall apart quickly,” Obama said.

“That’s what happened in Germany in the 1930s which, despite the democracy of the Weimar Republic and centuries of high-level cultural and scientific achievements, Adolph Hitler rose to dominate,” he continued.

“Sixty million people died. … So, you’ve got to pay attention. And vote.”

While some could see the remark as a veiled jab at Donald Trump, Barack Obama did not mention the president by name during the event, according to ChicagoBusiness.

Critics of Donald Trump say his rhetoric has fueled nationalist sentiment in the U.S. and anti-Muslim sentiment.