Not to be rude, but is this homework related?

The Taiping revolution's roots can be traced to a small Hakka minority in the Gunangdong region of China in the Southern part of the country. The Hakka were poor and were almost "second class' citizens to the ruling Manchus. The Hakka began to grow disillusioned with the Imperial Qing and began to rally around a village teacher named Hong Xiuquan. He claimed to be the son of the Christain God and was Jesus younger brother. He demonized the Manchu and called His message took hold of the Hakka minority and soon they were flocking to his banner. He preached a radical form of Christianity and egalitarianism.

The British at the start indirectly helped the Taiping rebels by attacking the Qing in the Second Opium war. After relations had cooled, the British saw that the Qing were better for business and, along with other western powers, began to support the Qing with weapons and ships, though some British MPs wanted to support the Taiping because of a shared Christian heritage. The Qing also made use of foreign mercenaries, like Charles Gordon.

Ultimately, the Taiping rebellion, along with the Nien Rebellion, helped accelerate the decline of the Qing empire and show how weak this once great empire had become. Future Chinese revolutionaries would rally around Hong Xiuquan and even anti-Christians like Mao Zedong would praise his attempts to overthrow the decadent Qing.

If you want to read more check out: A history of modern china by Jonathan Fenby, and Autum in the Heavenly Kingdom by Stephen R.Platt

Many causes. First, anti-Qing sentiment. The Qing were never beloved, as they were foreign invaders and viewed as usurpers to the throne. Although the Qing had become quite sinised by the 19th century (e.g. few of the bannermen spoke Manchu anymore), the Chinese were still reminded of this daily, such as in being force to have their hair in a queue. The Chinese had been forced to wear this Manchu hairstyle since 1644 as a sign of submission to Manchu rule. Secret societies like the Tiandihui existed, with an agenda to reinstate the Ming dynasty. (in reality this never seems to have made the top of their to-do list, but the ambition itself is witness to the anti-Qing sentiment).

Losing the first Opium War did of course not help. There was naturally outrage at this loss and the terms the Qing had accepted, accompanied by the loss of military strength, social upheavals and unrest, and the scourge of opium of course. Another factor Spence points out here is the westerners had used their naval power to drive the pirates away (threat to their trade after all), which pushed many of them to move to inland banditry, not least to the mountains of Guangxi, which is where the rebellion got started.

There was of course the introduction of radical new Christian ideas, aided not least by the free movement of missionaries being allowed by the peace treaty after the war. Although the contemporary Buddhist-Taoist tract the Jade Record seems to have had some influence on Hong Xiuquan as well.

It also had great populist appeal: They went against the authorities, against Confucianism, against the nobility. They promised a kind of proto-socialist redistribution of land and property. In short they targeted the disenfranchised and promised them a better future with better opportunities in the 'Heavenly Kingdom'.

Then, as Warband14 points out, there was a significant ethnic dimension as well. Hong Xiuquan was a Hakka, and the movement first caught on among that ethnic group. Elements of the Taiping doctrine - a ban on foot-binding, women workers and soldiers - likely came from Hakka custom (their women worked, they never practiced foot-binding). It might be pointed out that although they were indeed outsiders and lower in status than Han chinese, they still had a related language and weren't outsiders to the extent, say, the Miao were.

The Taiping relations with western natiosn were a bit ambivalent. Dissatisfaction with the Opium War was after all one of their recruiting points, but Hong obviously had an belief (of his own making) and respect for Christianity. This did not come to him through the British though; his main sources had been a Christian tract by Liang Fa and Gützlaff's bible translation. (which Hong later was to make his own changes to, removing some things he must have found disagreeable, such as Noah getting drunk - the Taiping had banned alcohol and opium) His bible instruction came from the American Baptist missionary Issachar Roberts, who later became one of the westerners advocating in favor of the Taiping - until he eventually fell out with them. Not least over the heterodox (to say the least) theology of the Taiping.

For most of its existence after the capture of Nanjing, the 'Heavenly Kingdom' was in a stalemate with the Qing. The Taiping's offensive campaigns (among others, north towards Beijing) had failed, but so did the Qing's. During that period they made repeated failed attempts to secure the westerners as allies, or at least their neutrality. Hong made a particularily fanciful attempt to recruit the 8th Lord Elgin, as he passed Nanjing (in a more well-known incident, Elgin was soon to burn the Summer Palace in Beijing)

Their last major offense was towards Shanghai. The western nations saw this as a threat to their trade and the international settlement (despite the Taiping's best attempts to reassure them that they and their property woudl not be harmed). But the westerners defended Shanghai, and you had the formation of the Ever Victorious Army and French Ever Triumphant Army, now taking an active role in fighting the Taiping. It was all downhill from there.

Again as Warband14 wrote, besides the devastation and millions killed, the Taiping rebellion was a significant factor in the demise of the Qing empire.

It does also play a certain role in Chinese Communist historiography. Regarding those populist demands for redistribution of land, Marx himself related a story from the translator of Hong's bible, Gützlaff:

When Herr Gützlaff came back among civilized people and Europeans after twenty years' absence, he heard talk of socialism and asked what it was. When he was told, he exclaimed in alarm: 'Am I nowhere to escape this ruinous doctrine? Precisely the same thing has been preached for some time in China by many people from the mob.'

This was in 1850, at the very start of the Taiping Rebellion, and while Marx noted that "Chinese socialism may, of course, bear the same relation to European socialism as Chinese to Hegelian philosophy.", and found it amusing that the western bourgoise had helped precipitate such a revolution, he expressed hopes for it as a 'socialist' revolution. (not unlike how other westerners projected their hopes for a Christian China onto them)

Marx did not write a great deal about them, but by 1862 he had apparently become as disillusioned with them as those hoping for a Christian revolution. He wrote:

They represent a still greater torment for the masses of the people than for the old rulers. Their motive seems to be nothing else than to bring into play against the conservative marasmus grotesquely repulsive forms of destruction, destruction without any germ of regeneration.

Marx's view of the Taiping is understandably, not that dissimilar from that taken by the Chinese Communists themselves, although the latter are perhaps less condemnatory.