Military is a collective noun. In American English, collective nouns are usually treated as singulars. The military has changed. In British English, collective nouns are usually treated as plurals. The military have changed.
Overall, the agreement of collective subjects and their verbs is goverened by regional usage and writer's choice.
"Collective nouns such as team and staff may be either singular or plural depending on their use in the sentence.
Examples The staff is in a meeting.
Staff is acting as a unit here. The staff are in disagreement about the findings.
The staff are acting as separate individuals in this sentence.
The sentence would read even better like this: The staff members are in disagreement about the findings."