"Beowulf" is an Old English epic poem consisting of 3.182 alternative lines. Although an exact date of publishing is not known, it is known that the poem was produced between 975 and 1025.
The parts of the passage shown in the question that indicate that the poem is about war and glory are the following: "Lo! the Spear-Danes'glory through splendid achievements. The Folk-kings' former fame we have heard of, How princes displayed then their prowess-in battle." This fragment is making allusion to previous wars that have been won, and how the glory conquered in them prevailed in time.
"Waxed 'neath the welkin, world-honor gained, Till all his neighbors o'er sea were compelled to Bow to his bidding and bring him their tribute." This fragment is making allusion about how honor was gained after the battle was won, and all the neighbors from over sea were forced to pay their respects to the winner, and send their tributes.