The striking expansion of Britain's geostrategic commitments and of its spheres of influence, occupation and rule had a less visible counterpart. There was at the same time a great widening and thickening of the web of commercial relations between Britain and many other parts of the world. This ‘commercial republic’ centred on the City of London, became one of the vital constituents of the British world-system that the late Victorians erected on its mid-Victorian foundations. Indeed, there was an obvious link between its extraordinary growth and the comparative ease with which the British world-system survived the stresses of geopolitical change after the mid-1870s. Britain's prosperity appeared to rise in direct proportion to the scale of its overseas trade and the increase of its invisible income. Income tax, estate duty, excise and postal receipts increased government revenues by nearly 50 per cent between 1870 and 1897. The favourable balance of payments (largely the product of invisible income) kept sterling strong and replenished the sources of investment abroad. The stream of outward-bound wealth, greasing and fuelling overseas commercial connections, was a powerful addition to British world influence. It secured Britain's claims on a huge range of assets, most of them safely remote from the great powers in Europe. It helped to sustain the flow of migration, Britain's demographic imperialism. Last, but not least, it preserved Britain's lead in communications technology, especially the telegraph and undersea cables that made London (and Britain) the information hub of the world.