I was a French protectorate for over four decades before gaining independence. My land is mostly desert, with a small part of it stretching along the Mediterranean coast. My capital is known for its white buildings and historic kasbah. I'm also known for an annual date festival. What am I?

1. My official language is Arabic, but French is widely spoken.
2. I share borders with Algeria and Libya.
3. My economy relies heavily on phosphate mining.
4. A major landmark is the ancient city of Carthage.