Leaders and their nations are paired in the following way:
1. Georges Benjamin Clemenceau was French Prime Minister during the First World War - France
2. David Lloyd George was the British statesman as well as the premier of the United Kingdom - Great Britain
3. Woodrow Wilson was American statesmen and 28th President of the US, among other things, was the President during the First World War - United States
4. Vittorio Orlando was the Italian statesman and prime minister during the final years of the First World War, represented Italy in the Paris Peace Conference - Italy
It is common for all of them that they were leaders during and around the First World War.