The speaker is stuck on something they can't make sense of, and the title, "Perplexed," says so plainly. The opening couplet plays with sound: "understand" and "stand" are tangled together, so the wish to understand something turns into an inability to bear it. Understanding and tolerating seem to be tied up in each other.
Then the mood shifts to exhaustion. The speaker feels "forced" to go to bed, as if sleep were a surrender rather than a rest. They hand the problem over to the night and ask it to "master" their mind, which sounds both tired and a little uneasy, since mastery suggests losing control.
The last image is the most striking: something "unfounded as a country / made for war." Judging by the wording, the speaker's confusion or fear may have no solid ground, yet it still feels like a place built for conflict. The poem leaves us in a restless, anxious, unresolved state.