The Brunei Gallery, SOAS is part of the University of London. SOAS is the School of Oriental and African Studies, and their current exhibit is called Empire, Faith, and War - The Sikhs and World War One. After I toured this I spent some time to learn more about Sikhism, and I think you should too.
The Sikhs soldiers were an important group in many battles of World War One. They valiantly fought for a country most had never seen. The Sikhs fought for their country in areas around Egypt, Turkey, and Palestine.
I was shocked by the following statistic posted at the exhibit:
"Although making up just 1% of the population of British India (concentrated mainly in the northern region of Punjab), Sikhs made up nearly 20% of the British Empire's Indian Army at the outbreak of the war."
The exhibit displayed different swords and military regalia along with moving photos of the soldiers in posed and candid situations.
This exhibit also showed many propaganda posters to promote support of Britain in the war.
A bonus to this museum is the Japanese garden on the roof. It is small, but it provides a nice solace in the middle of the city.
Admission to The Brunei Gallery, SOAS is free. It's open Tuesday through Saturday from 10:30am-5:00pm (Thursday until 8pm) and Sundays 11:30am-5pm
It is located right off green Russell Square, which gives you many options for the train: Russell Square (Piccadilly Line), Goodge Street (Northern Line), Euston Square (Metropolitan Line, Hammersmith & City Line, and Circle Line), Euston (Northern Line & Victoria Line) Tottenham Court Road (Central Line & Northern Line), Holborn (Central Line & Piccadilly Line), Warren Street (Northern Line & Victoria Line)