Article: Congo-Brazzaville has had a multi-party political system since the early 1990s, although the system is heavily dominated by President Denis Sassou Nguesso; he has lacked serious competition in the presidential elections held under his rule. Sassou Nguesso is backed by his own Congolese Labour Party (French: Parti Congolais du Travail) as well as a range of smaller parties.

Question: What kind of political system has existed in Congo-Brazzaville since the '90s?
multi-party