Overall, the United States is by far the most successful tennis country in history. Australia, France, and Spain have also had success, but none so consistent as the American team.
The Australian Margaret Court has the most Major singles titles, but Martina Navratilova has the most tennis titles. They were each the best in their own eras, as Serena Williams is in the current...
"Best" is a very qualitative statement, but if you look over the entirety of human history, the longest and most successful civilizations have been the Chinese and Indian. They have had a rough last...