GDANSK, Poland (AP) — The outbreak of World War II 75 years ago shows why Europe must put an end to the war in Ukraine now, Poland's prime minister said Monday.

Prime Minister Donald Tusk, chosen by EU leaders to be the next president of the European Council, spoke at the Westerplatte peninsula on the Baltic coast, where some of the first shots of World War II were fired on Sept.1, 1939, by the Nazi warship Schleswig-Holstein. Two weeks later Soviet troops invaded from the east, acting on a Moscow deal with Germany to carve up Poland.

More than five years of brutal, global war followed, taking the lives of almost 60 million people.

"Today, looking at the tragedy of Ukraine at war — because we should use this word — in the east of our continent, we know that September 1939 must not be repeated," Tusk said.

He said the lesson that Europe should draw from its past "must not be a lesson of naive optimism" because the continent's security requires "courage, imagination and resolute action."

Europe's security is the top priority for a NATO summit Thursday in Wales. Mindful of their painful history, Poland and the Baltic nations are calling for a sizeable, permanent presence of NATO troops on their territory, a goal that may prove hard to achieve.

"There is still time to stop all those in Europe and in the world for whom violence, force, aggression are again becoming an arsenal of political activity," Tusk said.

German President Joachim Gauck, also speaking at Westerplatte, called for the 28-nation European Union to "stand together."

"Stability and peace on our continent are in danger again," Gauck said. "We will oppose those who break international law, annex foreign territory and provide military support to breakaway movements in foreign countries."

His comments were a clear reference to Russia's actions in eastern Ukraine.