After Trump's election victory, former French president calls for a stronger European union.

• The election of President-elect Donald Trump has sparked concerns about an impending economic crisis for the European Union.
• Between 2012 and 2017, François Hollande, the former socialist leader of France, served as the nation's leader and briefly overlapped with Trump's first term.
• He recalled that Trump was often a man of his word.

The former French president emphasized the significance of European unity in countering U.S. protectionism on matters of security and commerce.

The election of President-elect Donald Trump has sparked concerns of an impending economic crisis in the European Union due to his promise to impose a 10% tariff on these countries.

Germany is facing an economic crisis and a political void, with concerns about the Ukraine war and the possibility of the U.S. withdrawing funding, leaving European allies to bear the financial burden.

Hollande told CNBC's Charlotte Reed Wednesday that Europe must be worried.

The U.S. disengaging from the European continent is a challenge that requires a response, according to the speaker.

The four main countries that invest in defense, namely France, Germany, Poland, and the United Kingdom, will act together to address security, the Ukraine issue, and the trade issue. If they do so, Europe will be respected. Otherwise, it will be pushed aside.

Hollande stated that even though Germany and France experienced political instability this year, there could still be a "broad political agreement" among major European countries, regardless of leadership changes, that would "strongly oppose what Donald Trump might do."

Ukraine peace?

Hollande, the ex-socialist president of France, governed the country from 2012 to 2017 and briefly overlapped with Trump's first term. He stated that Trump was typically trustworthy.

Trump has previously stated that he could "end the war" in Ukraine in 24 hours if elected, indicating that he would withdraw funding to force the country into a negotiated settlement with Russia. According to analysts, Ukraine could then be forced into a "bad peace" with its powerful neighbor, potentially resulting in the loss of almost 20% of its territory in the south and east, which is currently occupied by Russian forces.

Putin may be excluded from peace negotiations with Trump, which could allow Russia to retain its occupied territories.

"Hollande stated, "We must not let it happen because it would set a dangerous precedent where force has overpowered law.""

—CNBC's Silvia Amaro and Holly Ellyatt contributed to this article.