The poem is subtitled "Infantry Columns", and many of the words are printed multiple times to give the impression of marching and monotony.
A speaker says they are slogging over Africa and their boots – the word repeated four times –are moving up and down. There is no discharge in the war. They march miles and miles each day, and marched miles and miles the previous day. Their boots move up and down again and there is no discharge in the war.
The speaker intones not to look in front of you as the boots go up and down. Men will go crazy with watching the boots in front of them, and there's no discharge in the war. He says that you should try to think of something else to refrain from going crazy; the boots move up and down and there's no discharge in the war.
He says to count the bullets in the bandoliers and do not let your eyes drop or the enemy will get on top of you. The boots move up and down, and there is no discharge. He knows that they can withstand anything, including hunger, thirst, and fatigue, but that the unending sight of the boots is too much. The boots go up and down, and there's no discharge in the war.
It is not altogether too bad during the day because of one's friends, but at night the long strings of forty million are too much to bear. The boots go up and down, and there is no discharge. The speaker says he has marched six weeks down in Hell and can assert that there is no dark, or devils, or anything else – only the boots moving up and down again because there is no discharge from the war.
This poem, included in the 1903 volume The Five Nations, is one of Kipling's most charming, although the subject matter is not altogether lighthearted. It is known for its elocutionary emphasis, as reading it out loud requires some skill in making sure the meter and tone are adhered to just so. It is sing-songy, repetitive, and infectious. The repetition of the words over and over again reinforces the subject of the poem – that is, the endless marching of soldiers in wartime. It is a simple poem but a clever one; rarely does such a perfect harmony between form and subject exist.
The poem depicts soldiers marching throughout Africa for hours and hours, days and days. The soldiers hear and see and feel the boots of their thousands of companions without ceasing. They must try to avoid going crazy by thinking of anything other than this monotony. The monotony becomes even greater than starvation, dehydration, and fatigue. For the soldiers, the endless stomping of boots comes to signify the whole drudgery of war itself.
Kipling does an excellent job in this poem, as in many others (see "Gentlemen-Rankers" and "Tommy"), in presenting the various difficulties, great and small, in a soldier's life. Although not a soldier, Kipling understood the reality of the psychological, emotional, and physical duress suffered by the young men who went off to fight for their country. His own son John fought and died in WWI (and is perhaps immortalized in "My Boy Jack") and he embraced various causes that fought for good treatment for veterans.
There may be an actual subject of the poem, although it resonates universally. "Boots" may refer to the march of Lord Roberts's 60,000 men from Cape Town through Bloemfontein to Johannesburg, South Africa, in 1900. Kipling was well-versed in Britain's South African affairs and may be referencing them here. He visited and stayed there often; he supported the British actions in the Boer war and became a correspondent for a newspaper out of Bloemfontein.
Kipling had written of his being impressed with the idea of marching feet earlier in his career when he was a newspaper reporter for the Civil and Military Gazette in Rawalpindi, India. He wrote of "an infinity of booted feet coming down and taking up, with the exactness of a machine."