I want to know the answer to the following question:
What kind of political system has existed in Congo-Brazzaville since the '90s?
All the background I'm provided with is that "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.". Is that enough to answer the question?
Answer: yes