Why is Bengal’s 1905 partition seen as the road to 1947?

The short answer

• An administrative logic with a political edge. A province as large as Bengal presented a real administrative problem, but officials could have chosen among several boundaries. This line divided the Bengali-speaking intelligentsia leading nationalist agitation and cultivated East Bengal's Muslim majority as a counterweight. Divide-and-rule was not the whole explanation; the official record makes it part of the explanation. Congress and the League would both remember that an administrative map could be a political weapon.
• Swadeshi: the economy as battlefield. The boycott put Naoroji's economic critique of the Drain into action. British cloth imports into Bengal fell by a quarter in one year, and mills in Bombay and Ahmedabad boomed as demand shifted. Religious symbols and street theatre helped carry that economic nationalism into public life. A colonized society had found a way to hurt the metropole without a rifle. Gandhi watched closely from South Africa; Non-Cooperation would generalize Swadeshi.
• Muslim anxiety was real, not manufactured. The League's concerns cannot be explained away as a British invention, even though separate electorates were a gift from the Raj. Muslims were a quarter of India, poorer, and under-represented in universities and the professions. For many Bengali Muslims, Swadeshi's Hindu idioms, including Kali oaths and Bande Mataram, suggested that the awakening was not entirely theirs. Both perceptions were reasonable. The tragedy was that institutions built on them, above all separate electorates, made them permanent.
• Congress splits over method. At Surat in 1907 Congress divided over how to win reform. Gokhale's Moderates feared that pressure would cost them the reforms on offer; Tilak's Extremists held that agitation was the only way to obtain them. Tilak declared, “Swaraj is my birthright, and I shall have it”. The Raj jailed him for six years, settling the dispute in a way that proved his point. Later conflicts, Gandhi against the Swarajists and Congress against Bose, would replay Surat with higher stakes.

What it changed

The Raj learns retreat is possible — and so does India. The 1911 annulment was intended to buy quiet. It also gave later campaigns a precedent: sustained agitation could move London. The Raj had never reversed a major decision under Indian pressure; now it had done so, and the mystique of imperial finality never recovered.

Separate electorates: the wall in the foundation. Constitutionalists defended the 1909 separate electorates as minority protection. They also changed what a Muslim politician needed to win: Muslim voters chose representatives for Muslim seats, so moderation toward the other community won no votes and escalation cost none. Over time communal identity became the currency of politics. Nearly every historian of Partition treats the arrangement as load-bearing, whatever their other disagreements.

Delhi, the imperial capital — briefly. George V announced the move to Delhi personally at his 1911 durbar. The capital would leave Bengal's agitation for a city associated with the Mughal throne, presenting retreat in the form of imperial grandeur. Lutyens' New Delhi took twenty years to build; the Raj used it for sixteen. Its most magnificent capital passed to its successor state.