Former German Chancellor Angela Merkel has defended her record on handling Vladimir Putin in her first major interview since Russia invaded Ukraine.
She said she had "nothing to apologise for" over her response to Russia's annexation of Crimea from Ukraine in 2014, when she supported sanctions.
She also defended her opposition in office to Ukraine joining Nato.
Mrs Merkel has been accused of leaving Germany vulnerable by pursuing business-led relations with Russia.
The Nord Stream 2 pipeline to carry Russian natural gas directly to Germany was built while she was chancellor and only suspended by her successor, Chancellor Olaf Scholz, shortly before Russia invaded Ukraine on 24 February.
Under pressure to impose stringent new sanctions over the invasion, Germany is struggling to reduce its dependence on Russian energy without damaging its own economy.
But Mrs Merkel said Europe and Russia were neighbours that could not ignore each other. "We have to find a way to co-exist despite all our differences," she said.
The invasion was "not just unacceptable but also a major mistake by Russia", she told German journalist and author Alexander Osang in an interview televised by broadcaster ARD.
"If we start going back through the centuries and arguing over which bit of territory should belong to whom, then we will only have war," she said. "That's not an option whatsoever."
She defended the sanctions imposed on Russia in response to the annexation of Crimea and Germany's role in maintaining the Minsk peace process, which was meant to end the fighting in eastern Ukraine in 2014-15.
The peace process, she argued, allowed Ukraine time to develop as a nation and strengthen its military.
"I don't have to blame myself for not trying hard enough," she said. "I don't see that I have to say 'that was wrong' and that's why I have nothing to apologise for."
She had opposed Nato membership for Ukraine in 2008, she said, because she had wanted to prevent escalation with Russia and because Ukraine itself was not ready. "That wasn't the Ukraine we know today," she said. "The country was not stable, it was riddled with corruption."
Ukrainian President Volodymyr Zelensky, whose country remains outside the Nato alliance despite extensive Western defence aid since the invasion, has described Germany's decision in 2008 as a "miscalculation".
On Tuesday Mrs Merkel, who left office six months ago, said she had "the highest respect" for Mr Zelensky and was impressed by "the courage and passion" with which Ukrainians were fighting for their country.