Who inherited the austrian throne only after charles vi had the other european powers sign an agreement declaring they would recognize the heir?

Maria Theresa

Explanation:

As his only son died early, Charles VI bequeathed his inheritance to his eldest daughter, Maria Theresa. Fighting strenuously to wrest agreement from the European powers, he seemed at the time of his death to have accomplished his purpose. But his expectation proved illusory: Maria Theresa was forced to fight several wars before she could establish herself securely as her father's heiress.