While Shivaji did espouse the Hindu cause,it cannot be rationalized in terms of nationalism as we understand in this age and time,while obvious similarities exist,but they must not be overemphasized.The scope and scale are vastly different.
While Shivaji did take up cudgels against the Shia sultanates of the Deccan and later the Mughals and the ill treatment of the Hindu peasantry(esp Maratha)was one salient cause.Shivaji was quite less bellicose against the Portuguese,who dominated the Konkan coast and were no less cruel in persecuting Hindus(although rampant and violent conversions being carried out by Portuguese brought some friction between the two.
Remember Shivaji even went to The durbar of Aurangzeb for recognition and reconciliation,who knows, hadn't Aurangzeb been stupid enough to instead imprison him,things may even have turned out differently.Shivaji's bloody campaigns were not just against the Mughals and Adil Shahis,many of his enemies were fellow Hindus,perhaps even kinsmen.
Shivaji's conquest of Javli,his first big conquest which established him as a player in the region,came about under dubious circumstances.Shivaji probably orchestrated a coup and had Chandra Rao More,the ruler of Javli,executed. Its a different matter that Mores would have done the same to Shivaji, if presented with an opportunity,Shivaji was only tactically more clever.
Shivaji belonged to apolitical class,whose control over their traditional lands and title had rapidly eroded under the Sultanates and later the Mughals.The order that was established under Akbar had been totally upturned under a puritan Aurangzeb,The Mughal invasion of Deccan Shia sultanates had seriously weakened the Deccan Shahis and this presented a perfect opportunity to the traditional feudal houses to reassert the their lost power.
Shivaji was unarguably more successful in this endeavor.
