Russia was deemed the world’s undisputed leader in:
Multiple launch rocket systems
Artillery, both towed and self-propelled
Mine/countermine warfare ships
The index, which also takes resources and logistics into account, notes that Russia is number one in the world in terms of total square land area coverage and proven natural gas reserves.
Notably, the GFI does not include nuclear arsenals into its calculations.
The other four nations that made the world’s top five military powers according to GFI are China, the United States, India and South Korea.