Final answer:
The Estates-General meeting was unfair to the Third Estate because the voting system favored the first and second estates and gave them more power. The Third Estate declared themselves the National Assembly to fight for the people's interests.
Step-by-step explanation:
The Estates-General meeting was unfair to the Third Estate because the voting system followed medieval rules that favored the first and second estates. Each estate had one vote, which meant that the Third Estate, representing 97% of the population, had the same voting power as the other two estates combined. This system allowed the clergy and nobility to consistently defeat any initiatives proposed by the Third Estate. The unfairness of this system led the Third Estate to declare themselves the National Assembly and take action to govern in the interests of the people.