The root cause of Sikh migration was economic due to extractive policies and repression of the British Empire.
The Second Sikh Kingdom (1799-1849) of Maharaja Ranjit Singh was swallowed up by the larger geopolitical tide of colonization by the British Empire and the hunger for resources for the first industrial revolution.
British Professor Leitner evaluated Punjab’s indigenous education system setup by the Sikhs. "Respect for learning has always been the redeeming feature of ‘the East’. To this the Punjab has formed no exception.” “…Oriental literature and systems of Oriental Law, Logic, Philosophy, and Medicine were taught to the highest standards." "Through all schools there breathed a spirit of devotion to education for its own sake and for its influence on the character and on religious culture;" (Leitner, 1883)
"The true education of the Panjab was crippled, checked, and is nearly destroyed; how opportunities for its healthy revival and development were either neglected or perverted; and how, far beyond the blame attaching to individuals, our system stands convicted of worse than official failure." (Leitner, 1883)
This is universally true. Traditional values and education instill "discipline, self-confidence, and moral and social values". They are not visible through modern lenses, but are visible with the right perspective. Destroying people’s education system, philosophy, way of life, and distorting history is done because once they are destroyed, people remain subservient, and their land and resources can easily be looted.
"The British authorities in the Punjab taxed Sikhs not in kind as the Sikh Kingdom used to, but in cash, so that a sharp fall in crop prices led to the bankruptcy of many peasants who failed to sell their products in the markets at a good price." (Cao Yin, ‘From Policemen to Revolutionaries: A Sikh Diaspora in Global Shanghai, 1885–1945’, p.63) Sikhs had to migrate to Shanghai, Hong Kong, and Singapore as policemen. Sikh farmers went to East Africa and USA, and Sikh woodsmen to Canada.
British Empire destroyed Sikhs by destroying their language and culture by destroying their education system; destroyed their agriculture (by taxing in cash rather than in kind as a percentage of produce); destroyed their industry (Wootz steel industry), and more.
Sikhs were not merely 'Yes-men' or hired policemen or soldiers or mercenaries. They were a civilizing influence wherever they went. They “were not merely responsible for checking riots and crimes, but also for carrying out the civilizing project in the International Settlement; on the other, they frequently challenged the authorities that they thought to be oppressive and discriminative." (Cao Yin, ‘From Policemen to Revolutionaries: A Sikh Diaspora in Global Shanghai, 1885–1945’, p.23) They were an equal partner in 'civilizing projects' and a check on oppression and discrimination by the authorities.
It is important to note that Sikhs never held or hold any grudges or hatred towards the British even with full knowledge that the British had systematically and knowingly destroyed their empire, their education system, their culture, their agriculture, their industry, massacred more than 1000 unarmed peacefully protesting Sikhs in cold blood with machine guns till they ran out of ammunition at the Jallianwala Bagh massacre in 1919 in Amritsar, and kidnapped Maharaja Ranjit Singh’s heir to the throne Maharaja Duleep Singh to England.
Winston Churchill said “British people are highly indebted and obliged to Sikhs for a long time. I know that within this century we needed their help twice and they did help us very well. As a result of their timely help, we are able to live with honour, dignity and independence.”
A more recent publication summed up views about Sikhs: "Read your history. Sikhs are defenders - not destroyers - of Western civilization." (Jim Beckerman - northjersey.com, 2018)
The root cause of Sikh migration was economic due to extractive policies and repression of the British Empire.