Answer: All the kingdoms have the same rule.
Step-by-step explanation:
The term "has" may imply that the subject: kingdom(s) is singular, not plural.
However, this is clearly not the case. The word "All" and the "s" at the end of kingdoms express a sense of plurality, which implies that it is "All the kingdoms have the same rule."
When reading the following statement, along with any other statements of this particular medium, it is always best to look for flow as well. If the filled in word makes the sentence sound choppy, it may not be the right word for the sentence.