It's a nuanced film made about a complex subject produced before everything got consumed by the culture wars. I don't think it supports or condemns imperialism, it praises the bravery and warrior spirit displayed by both sides.
The British and the Zulus (and the Boers) were trying to expand their empires in the south east of Africa. They clashed during the Anglo-Zulu War which the British eventually won. However, as with many imperial wars at the time, the whole thing was a bit of a cluster fuck by the British. We were using rifles against leather shields so we should have won easily. Arrogance and incompetence put paid to that and the war, though brief, was far more costly from a British point of view than it should have been.
The film depicts the Battle of Rorke's Drift. The British had recently suffered humiliating defeat at the Battle of Isandlwana and the Zulus then marched on the guarded missionary outpost at Rorke's Drift. During the battle, 150 British soldiers defeated over 3000 Zulu warriors so it was rightly hailed as a great victory. More Victoria Cross medals (Britain's highest military honour for bravery) were handed out then that at any other battle. The battle became enshrined in British folklore forever more.
Because Britain industrialised before any other nation we found it comparatively easy to form such a vast empire. As such, we were often a bit embarrassed by the ease with which we were able to conquer the world and sought examples of 'against the odds' heroism to justify our position. The Charge of the Light Brigade, General Gordon in Khartoum and the Battle of Rorke's Drift were all the result of incompetence in one way or another. However, they all allowed us to say to the world (and ourselves) 'hey, look at brave little Britain staring death in the face and remaining stoic in the face of insurmountable odds'. The Second World War / Battle of Britain was a genuine example of this and helped to cement this quality as part of our national identity.
The film was made with the collaboration of the Zulu chief at the time and most of the African actors in it were real Zulus. As far as I'm aware they were happy with the way they were depicted and were well paid for their work.
To be honest, I find most of the film pretty boring. It drags on for hours with not much happening. You can get the message that they are trying to convey by just watching the final battle scene which is, in my opinion, one of the best ever filmed.
TLDR, just watch this:
