He specialized in American colonial and revolutionary-era history, looking at merchants, demographic trends, Loyalists, international links across the Atlantic, and especially the political ideas that motivated the Patriots.

He argued that international commerce was an uncertain business, given the high risk of losses at sea in the very long turnaround times, which meant that information was often too old to be useful.

Like Edmund Morgan at Brown University and Yale, Bailyn emphasized the multiple roles of the family in the colonial social system.

He located the intellectual sources of the American Revolution within a broader British political framework, explaining how English country Whig ideas about civic virtue, corruption, ancient rights, and fear of autocracy were, in the colonies, transformed into the ideology of republicanism.

According to Bailyn, The modernization of American Politics and government during and after the Revolution took the form of a sudden, radical realization of the program that had first been fully set forth by the opposition intelligentsia ... in the reign of George the First.

Where the French opposition had vainly agitated for partial reforms ... American leaders moved swiftly and with little social disruption to implement systematically the outermost possibilities of the whole range of radically libertarian ideas.

[10]In Bailyn's assessment, contested libertarian meanings change through time as "the colonists" struggled to define, and to pursue, the property of independence.

Recent historians hold that more than any other "colonist," Boston waterfront rebels channeled their "cosmopolitanism into a belief that 'the cause of America' was a libertarian 'cause for all mankind.

"[11] In her memorial tribute, Harvard historian Joyce Chaplin noted Bernard Bailyn's resistance to "dichotomies" and his attention to "granular" records and culture.

[12] In that context, Bailyn did not publish on political philosopher Isaiah Berlin until a 2006 assessment of "perfectionist ideas" found in "Two Concepts of Liberty."

But their threat to civilisation, in the most general terms, lay not in their intrinsic malevolence but in the brutality of those who implacably imposed them: the populist thugs, the fanatical monopolists of power.

His histories of the peopling of colonial North America explored questions of immigration, cultural contact, and settlement that his mentor Handlin had pioneered decades earlier.

[15] Bailyn's Atlantic History: Concepts and Contours (2005) explores the borders and contents of the emerging field, which emphasizes cosmopolitan and multicultural elements that have tended to be neglected or considered in isolation by traditional historiography dealing with the Americas.