Politicians, military officers and diplomats from around the world gathered in Munich on Friday to discuss Europe's security situation following the Russian invasion of Ukraine almost a year ago.
The war has reignited long-running debates on questions such as how much Europe should build up its own military capacity, how much it should rely on the United States for its security, and how much governments should spend on defence.
Delegates to the Munich Security Conference, an annual gathering focused on defence and diplomacy, will also discuss the global impact of the war on issues ranging from energy supply to food prices.
German Chancellor Olaf Scholz, French President Emmanuel Macron and U.S. Vice President Kamala Harris are among those attending the conference, which begins on Friday and runs until Sunday. Senior Ukrainian officials are also expected to address it.
Setting out Kyiv's position, an adviser to Ukrainian President Volodymyr Zelensky said "real global security" could only be achieved if Ukraine won the war.
"Negotiations can begin when Russia withdraws its troops from the territory of Ukraine. Other options only give Russia time to regroup forces and resume hostilities at any moment," Mykhailo Podolyak wrote on Twitter.
Last year's conference took place just days before the war began.
As Russian troops massed on Ukraine's borders, Western leaders in Munich urged President Vladimir Putin not to invade and warned of dire consequences if he did so, while Zelenskiy criticised what he saw as appeasement towards Moscow.
This year, leaders will grapple with the profound consequences of Putin's decision to ignore their pleas and unleash the most devastating war in Europe since World War Two.
"If Putin wins in Ukraine, the message to him and other authoritarian regimes is that force is rewarded," NATO Secretary-General Jens Stoltenberg said this week.
"That would make the world more dangerous. And all of us more vulnerable," Stoltenberg said.
He was speaking ahead of a meeting of NATO defence ministers, who pledged to increase military supplies to Kyiv even as they admitted their own munitions stockpiles have been badly depleted by the war.
German Defence Minister Boris Pistorius repeated his pledge for Berlin to exceed NATO's 2% military spending target.
"We will make every effort to go beyond it, though this still needs to be agreed within the (ruling) coalition. But it has to be clear to everyone that, with scarcely 2% only, we won't be able to meet the challenges that lie ahead," he said as he arrived for the conference.
The conference has sometimes served as a barometer of relations between Russia and the West, most notably in 2007 when Putin criticised the United States in a speech now widely seen as a harbinger of a far harsher stance against liberal democracies.
This year, Russian leaders will be notable by their absence.
Conference chair Christoph Heusgen, a veteran German diplomat, said organisers had not invited any Russian officials as Putin had "broken with civilisation".
However, Moscow made its voice heard from afar, accusing Washington of inciting Ukraine to escalate the conflict and saying that the United States was now directly involved in the war because "crazy people" had dreams of defeating Russia.
A U.S. delegation of record size is expected at the conference, including Harris, Secretary of State Antony Blinken and a third of the U.S. Senate.
"We expect a signal of unity from the transatlantic community," Heusgen told reporters.
The conference will also highlight to Western leaders that much of the rest of the world does not see things their way.
Efforts to get African, Asian and Latin American leaders to isolate Moscow have often floundered, due to Russian diplomatic and economic clout and anger in the Global South that the West has shown far less interest in conflict and injustice there.
Other big international issues will also feature at the conference, particularly relations between the West and China.
Top Chinese diplomat Wang Yi is expected to attend and Blinken is considering meeting him there, in what would be their first face-to-face talks after the United States shot down what it said was a Chinese spy balloon and other flying objects.
More than 40 heads of state and 60 ministers were expected to attend the conference, which coincided with a day of mass strike action at German airports including Munich. While government planes could land at the airport, delegates travelling on commercial flights faced disruption.
