What was one significant outcome of the Thirty Years' War? O A. European rulers agreed to respect one another's right to choose
their kingdoms' religion.
B. Religious conflicts between Catholics and Protestants increasingly
evolved into bloody wars.
O C. European monarchs agreed to establish constitutions that would
limit their authority.
O D. The Catholic Church agreed to greatly reduce its influence over
European political leaders.

A. European rulers agreed to respect one another's right to choose their kingdoms' religion

Explanation:

The Thirty Years' War was a war of religion that took place in the Holy Roman Empire, which comprises of four kingdoms, between 1618 to 1648, and concluded with the Peace of Westphalia in 1648

The Peace of Westphalia which officially introduced the model of peace being arrived at through a congress of diplomacy and new European political order that is founded on the principle of sovereignty of co-existing states and acceptance of the sovereignty of other states and a states right to decide its fate, principles of which are the founding bases of the present day international law

Therefore, a significant outcome of the Thirty Years' War is the agreement by European rulers to respect the right of one another to decide the religion of their kingdom

ask google there you might be able to find an answer for the question you're trying to ask

ok sorry the answer is a. by their religion