To understand Sikhism you have to understand Hinduism. Hinduism is not Christianity and Islam which are codified religions, and have a book and a prophet. Hinduism has originated from various rituals tribal customs and social life over the centuries. Hinduism has 1000?s of Gods and Goddesses and various diverse thoughts.
Predominant amongst these thoughts is a way of life called Sanatan Dharma which more than 60% of the Hindus follow, and this is generally mistaken as Hinduism, and the other thoughts are treated as offshoots of Hinduism. The real truth is that Hinduism means Sanatan Dharma AND all the other thoughts. Sikhism is but one of these thoughts.
Firstly, the British with their policy of divide and rule, and secondly, political turmoil and hatred between Hindus and Sikhs has put the idea of a separate identity in the mind of us Sikhs. Many of my co-coreligionists will say ? but we have different ideas as compared to Hinduism. Sure - I agree that we are different in ways but there are 50 ? 100 major different thoughts within Hinduism and we are BUT one of them.
Do you understand ? Whereas fundamentalist Sikhs we say that we are 1 amongst 7 great world religions the fact is that there are actually 4 great religions. One - Christianity has various branches - Catholic, Protestant, Methodist, Adventist, etc. Second ? Islam has various branches - Shia, Sunni, Ahmediya etc. There is Judaism and finally Hinduism ( which is a collection of various beautiful thoughts like Buddhism, Sanatana Dharma, Sikhism, Jainism, Arya Samajists, Vaishnav, Shaivaites Manbhum, Santhal etc )
So Sikhism is born out of Hinduism. Guru Nanak was born a Hindu, he was a traveling holy man who followed a custom of Sant Mat ( or Saint Tradition ) quite popular amongst saints those days. It was a thought he inculcated in his believers and told them to learn it. His believers were called Sikhs as Sikh means ? ?to learn? We had 9 more Gurus. Yes Guru Nanak also took some minor feedback from Islam but that is the nature of Hinduism ? to absorb from everyone.
EDIT - Steelboy is a sikh fanatic who does not understand that both Buddhism and Sikhism like Christianity and Islam have plenty of foolish references.
Guru Nanak squeezed one roti and turned it into milk and another roti into blood. While Guru nanak slept a cobra shaded him from the sun. There is the kauda demon miracle, the buffalo grazing miracle, the panja sahib miracle..........Then Baba Deep Singh picked up his severed head in his right hand and continued to fight with his left.........Many Sikhs keep our hair unshorn since our birth and wearing 6-9 metres of cloth wrapped around our heads in India's Summer heat is faith to Sikhs but a meaningless - nay abnormal ritual to others?
All religions have foolish references. But that does not mean that the roots of Hinduism and Sikhism are different just because both religions have various and diverse stupid ideas which are part of their history and culture.
Both these religions reject Vedas and Brahman.So for Hindus who know their books both are Malechhas(word meaning very similar to gaffer). Both Buddhism and Sikhism do not believe in Agni rickshaw of Sita(placing a lady in fire to test her purity). Both Buddhism and Sikhism do not believe in cutting nose of a woman who expresses love towards a man(story of Sroopnakha and linesman). Both Sikhism and Buddhism do not believe in this quote of Ramayana Drums, villagers, low caste, animals and women deserve beatings. Both Sikhism and Buddhism do not believe in steeling(Story of steeling of Parjaat tree from heaven and steeling of clothes of ladies having bath for fun). Both Sikhism and Buddhism ridicule this thought that a person whose status is high as god can fall in love with his own daughter(Story of Brahma). Both Sikhism and Buddhism do not believe that Hanuman was a monkey and Ganesha carried elephant head. Sikhs and Buddhists also do not believe that Shiva drank Cannabis.
Edit: Oops I also attack meaningless rituals in Sikh religion and can tell rationale behind them. You either say my points are true or wrong, do not indulge in stupid arguments. If you have any thinking, you should have started thinking why you are claiming as Sikh. You can not think because only a sane can think.
Four Purushaarthams(objectives of life) are (1)Dharmam=duty towards kith & kin,Guru,friends,society,country,world etc----(2) Kaamam =love,affection,emotional attachment,patriotism etc---(3) Artham=material wealth--these 3 are common for Sanathana Matham(Hinduism),Buddism,Jainism,Sikhism--the 4Th one namely Moksham or Mukthi=salvation is same for Hinduism and Sikhism--but not for Buddhism,who follw "Nirvaana" concept.Buddhists do NOT beleive in the existence of a "Supreme Being"(Brahmam)--Hindus and Sikhs beleive in Brahmam.The word Brahmam is repeated several times in Guru Granth Sahib(Sacred Sikh Religious text)--According sri.Vyaasa's School,any person who beleives in Brahmam, the "essence"/"Spirit" of Vedham is an Aasthika (Theist) akin to a Hindu("Saastra Yonivat").Buddhists do not beleive in Brahmam,so they are dubbed as Naasthika(Atheist)--so one can see who is "more like"