King Louis XVI ready to use force against the 3rd estate because he was afraid to lose power so he threatened to make a foreign army to keep his power.
Also there is a problem with this was the First and Second Estate made up only 3% of the population of France while the Third Estate made up 97% of the population.The vote, therefore, would not truly represent what the people wanted if the Third Estate was always outvoted.
The third estate had to pay the taxes and they alone bore the expenditure for France. The nobility used up the tax money and war costs and debts forced the king to increase taxes at a time when France was in a subsistence crisis.
Third Estate was unhappy with the old rules of voting because they believed that it unfairly favored the privileged classes and limited their political power.