With US President Donald Trump back, Europe must "sit at the main table and safeguard our interests vis-a-vis Russia and China", Merz told the campaign rally in Munich.
Europe's biggest economy goes to the polls on Sunday after a campaign marked by high US-Europe tensions after Trump ended a united Western stance on the Ukraine conflict by reaching out to Russia.
Europeans have scrambled to respond to the shock move and to ensure they and Ukraine are not sidelined in any potential talks to end the war.
"Europe must become stronger again and Germany must become more involved in the European Union," said Merz, who is widely expected to beat centre-left Chancellor Olaf Scholz, according to the polls.
"Every election is a pivotal election, a historic election," Merz told the rally of his CDU/CSU alliance.
But he pointed to the special "circumstances under which this election will take place tomorrow", to "what we are currently experiencing in the world" and what it could mean for the post-war order.
"None of us can be sure today that what we have had for 75 years will continue for the next 20 to 30 years, and that is why this election tomorrow is a pivotal election for Germany."
Merz's CDU/CSU alliance is leading in the polls ahead of the election on around 30 percent, double the score for Scholz's SPD, and with the far-right AfD in second place on around 20 percent.
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