Turkey’s geography and membership in NATO have long given the country an influential voice in foreign policy, but the assertive policies of President Erdogan have complicated its role.

The Group of Seven (G7) serves as a forum to coordinate global policy, but experts are increasingly questioning the group’s relevance.

The Group of Twenty, an informal gathering of many of the world’s largest economies, is the premier global forum for discussing economic issues. But it has faced divisions over trade, climate change,…