While this may be a poem about heading off to war, it takes place decidedly on the home front. After all, our speaker is still trying to explain himself to Lucasta, who's definitely not headed into battle.
If we zoom out a bit, we'll remember that Lovelace was writing during the English Civil War, when it's likely that a fair amount of men were leaving their loved ones to go duke it out in battle. So the poem does seem rooted in a specific historical setting.
And yet. We think it's more universal that that. Lucasta, while she may be a specific woman to Lovelace, could be just about any woman who's been left behind at home while her main man heads off to war. In that sense, the specific historical setting fades into the background to let the universal themes of love and sacrifice shine through. There will always be wars, and there will always be Lucastas left behind.