The same that stops them from taking over a democracy. Sometimes.
If a society became anarchist enough to abolish state structures, there obviously had to exist a reason - there had to exist popular support.
Thus, someone attempting to recreate a state would face questions and opposition. People would try to persuade them of their error. If they declared a state, anarchists would not recognize it. If it claimed sovereignity above a territory, anarchists might not recognize that either.
The new state might encounter problems - unwilling residents would leave and be accepted in anarchy, annoyed anarchists would organize trade boycotts and sanctions, ultimately it could go badly and armed confrontation could follow. In some scenarios, the state might remain and attract people who want to live there. In some scenarios, war would follow - and if the majority really was anarchist, the state would lose and disappear.