Dayanand Saraswati visited Punjab in 1877 and the Arya Samaj took root there faster and deeper than anywhere else in India. By 1900 Punjab held the majority of its membership.
It built the DAV school and college network, which educated a large part of urban Punjab's Hindu population and a good many others. Lala Lajpat Rai came out of it.
It also ran shuddhi, reconversion, which targeted Muslims and Christians and set off a cycle of competitive proselytisation. Its polemics against Sikh practice, and Dayanand's own remarks on Guru Nanak Dev Ji, provoked the Singh Sabha response and the writing of Ham Hindu Nahin.
The Arya Samaj, the Singh Sabha and the Anjuman-i-Islamia were all reform movements of the same generation, all working through print, schools and public debate, and all of them sharpened the boundaries between communities that had been much less sharply drawn.
The census categories of colonial Punjab and the reform movements' definitions of who belonged to what fed each other. By 1947 the province was thought of by everyone as three communities, and it had not been in 1847.
The Arya Samaj was founded in Bombay and had its greatest success in Punjab, where its schools, its shuddhi campaigns and its polemics reshaped Punjabi Hindu identity.
The DAV college network it built is one of the largest private education systems in India and it began at Lahore in 1886.
Its argument with the Singh Sabha over whether Sikhs were Hindus is the direct cause of a great deal of what followed, including Ham Hindu Nahin and the whole Sikh identity literature of that period.