TOKYO -- Leaders of seven of the world's most powerful democracies will gather this weekend for the Group of Seven summit in Hiroshima, the location of the world's first atomic attack at the end of the Second World War.

From the emergence of crucial developing countries to security worries, including growing aggression from China, North Korea and Russia, here's a look at the G7, who will attend and some of the key issues:

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WHAT IS THE G7 SUMMIT?

The Group of Seven is an informal group of leading industrialized nations. It consists of Canada, France, Germany, Italy, Japan, the United Kingdom and the United States.

This year is Japan's turn to host, but the presidency of G7 summits revolves among the seven members. Two representatives of the European Union also join.

As is customary in recent years, leaders from some non-G7 countries and international organizations will also participate in some sessions.

The leaders discuss a wide range of issues, including economic policy, security, climate change, energy and gender.

The first summit was in 1975, when France hosted what was then a Group of Six meeting to discuss tackling a recession that followed an Arab oil embargo. Canada became the seventh member a year later. Russia joined to form the G8 in 1998 but was expelled after Moscow's 2014 annexation of Crimea.

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WHO ELSE IS COMING?

This year, the leaders of Australia, Brazil, Comoros, Cook Islands, India, Indonesia, South Korea and Vietnam are invited, as Japanese Prime Minister Fumio Kishida stresses the importance of reaching out to developing countries in the so-called Global South and U.S. allies and partners.

The invitations to leaders outside the G7 are meant to extend cooperation to a broader range of countries.

The G7 countries' share of global economic activity has shrunk to about 30% from roughly 50% four decades ago. Developing economies such as China, India and Brazil have made huge gains, raising questions about the G7's relevance and its role in leading a world economy that's increasingly reliant on growth in less wealthy nations.

Leaders of the United Nations, the International Energy Agency, the International Monetary Fund, the Organization for Economic Cooperation and Development, the World Bank, the World Health Organization and the World Trade Organization are also invited.

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WHY HIROSHIMA?

Hiroshima is Kishida's hometown. His choice of venue underscores a determination to put nuclear disarmament and non-proliferation at the top of the agenda of this year's summit.

A path to nuclear disarmament has appeared more difficult with Russia's recent nuclear weapon threats in Ukraine, as well as nuclear and missile development by China and North Korea.

Japan, which is protected by the U.S. nuclear umbrella, has also faced criticism that its nuclear disarmament pledge is an empty promise. Kishida is trying to forge a realistic roadmap between the current harsh reality and the ideal of a world without nuclear weapons.

Kishida on Friday will welcome arriving leaders at the Hiroshima Peace Park. He also plans to escort the leaders to the A-bomb museum, in the first group visit by heads of nuclear states. There might also be a meeting with atomic bomb survivors.

"I believe the first step toward any nuclear disarmament effort is to provide a first-hand experience of the consequences of the atomic bombing and to firmly convey the reality," Kishida said Saturday during a visit to Hiroshima to observe summit preparations.

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WHAT ARE THE TOP ISSUES?

G7 leaders are expected to strongly condemn Russia's war on Ukraine while pledging their continuing support for Ukraine. Ukrainian President Volodymyr Zelenskyy will join the session via the internet.

There will also be a focus on Beijing's escalating threats against Taiwan, the self-governing democratic island Beijing claims as its own, and ways to reduce Western democracies' economic and supply chain dependency on China.

To address the rise of Global South nations, including many former colonies of Western powers with varied views on and ties to Russia and China, the G7 will offer these countries more support in health, food security and infrastructure to develop closer ties.

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WHAT ELSE IS HAPPENING?

In a closely watched event on the sidelines of the summit, Kishida will meet together with U.S. President Joe Biden and South Korean President Yoon Suk Yeol to discuss closer security cooperation, possibly including stronger nuclear deterrence.

Kishida and Yoon will pay their respects together at a Hiroshima memorial for Korean atomic bomb victims in a trust-building gesture as the two countries repair ties strained by disputes stemming from Japan's 1910-1945 colonial rule of the Korean Peninsula.