President Biden’s trip to Europe includes a rare day of three consecutive world summits on Thursday as world leaders gather in a variety of forums to discuss their response to Russia’s war in Ukraine.

NATO: Thursday morning, Mr. Biden joined the leaders of the 30 countries that make up the North Atlantic Treaty Organization, a group formed after the Second World War to promote a common defense. On the agenda: whether and how to provide more robust weapons to Ukraine and how to strengthen NATO’s own defenses in Poland and along the eastern front with Russia.

Mr Biden and the others were also expected to discuss grim scenarios of a possible further expansion of Russian attacks in NATO countries, and how the alliance would respond.

G7: After the NATO rally, Biden will join leaders of the Group of 7, the world’s largest wealthy democracies, to continue the discussion on Ukraine. The meeting, which includes the leaders of Britain, Canada, France, Germany, Italy, Japan and the United States, was convened by German Chancellor Olaf Scholz, who is the current president of the G7.

The group is expected to confront the refugee crisis sparked by millions of Ukrainians fleeing Russian forces and discuss what more the world can do to punish President Vladimir V. Putin for his aggression.

European Council: Mr. Biden will then cross Brussels to join the 27 leaders of the member states of the European Union. The summit, known as the European Council, was the long-planned regular meeting of EU leaders that takes place quarterly, but Mr Biden was invited due to the bloc’s close coordination with the United States on sanctions and all other measures in response to Russia’s request. invasion of Ukraine.

The group will likely focus on expanding sanctions as well as pushing Mr. Scholz to step up enforcement to ensure Russia is not able to escape the pain of the sanctions. EU leaders will continue their meeting on Friday, after Mr Biden leaves for Poland.

Overlapping Memberships: Both NATO and the European Union have their headquarters in Brussels and their origins in the years following World War II, but the differences between them are significant. NATO was built as a military bulwark against Soviet power, while the European Union is a political and economic bloc that grew out of efforts to unite the once-warring nations of Western Europe through the trade.

Twenty-one countries now belong to both, including a swath that once fell under the Soviet sphere of influence. But the EU’s 27 members include several countries that have remained outside NATO, often due to traditions of neutrality, such as Austria, Ireland and Sweden. Among NATO’s 30 members are the United States, by far its dominant military partner, and Canada, as well as several countries that have left or refused to join the European Union (Great Britain, Iceland , Norway) or have applied to join (Albania, Montenegro, North Macedonia, Turkey).

The Group of 7, on the other hand, was formed during the economic upheavals of the 1970s to facilitate discussions between the leaders of the most powerful economies in the Western world; it now includes leaders from the European Union, alongside those from Britain, Canada, France, Germany, Italy, Japan and the United States.