"在军事上" can be translated as "militarily" or "in the military sphere/context/aspect".
"Militarily" is often used as an adverb to describe actions or situations related to the military, e.g., "Militarily, the country has made significant advancements."（在军事上，这个国家取得了重大进展。）
"In the military sphere/context/aspect" provides a more detailed description, emphasizing the specific domain or context, e.g., "In the military context, this strategy is highly effective."（在军事上，这个战略非常有效。）