Technology made the new imperialism possible. It vastly increased the speed of communication, it armed European soldiers with advanced weapons that overwhelmed resistance, and it protected Europeans from tropical diseases. Simply put, technology explains how European dominance grew from about 35% of the globe to over 80% over the course of the nineteenth century. In hindsight, European technological dominance was nothing more or less than a historical accident, the circumstantial development of tools and techniques that originated with the Industrial Revolution. At the time, however, most Europeans and Americans considered their technology as proof of their “racial” and cultural superiority.
For example, for the first time cities in Europe acquired the means to communicate almost instantaneously (via telegraph) with their colonies. Before telegraphs, it could take up to two years for a message and reply to travel between England and India, but after telegraph lines were constructed over the course of the middle decades of the nineteenth century, a message and reply could make the circuit in just two days. This, of course, vastly increased the efficiency of governing in the context of global empires.
Europeans were not just able to communicate with territories thousands of miles away thanks to technology - they could survive there as well. Africa had never been colonized by Europeans before the nineteenth century, except for relatively small territories in along the coasts. The continent was largely impenetrable to Europeans thanks to its geography: there were few harbors for ships, the interior of the continent had no rivers that were navigable by sail, and most importantly, there were numerous lethal diseases (especially a particularly virulent form of malaria) to which Europeans had little resistance. Until the second half of the century, Africa was sometimes referred to as the "white man's graveyard," since Europeans who travelled there to trade or try to conquer territory often died within a year.
That started changing even before the development of bacteriology. In 1841, British expeditions discovered that daily doses of quinine, a medicine derived from a South American plant, served as an effective preventative measure against the contraction of malaria. Thus, since malaria had been the most dangerous tropical disease, Europeans were able to survive in the interior of Africa at much higher rates following the quinine breakthrough. Once Pasteur's discoveries in bacteriology did occur, it became viable for large numbers of European soldiers and officials to take up permanent residence in the tropical regions of Africa and Asia.
Advances in medicine were joined by those in transportation. The steamboat, with its power to travel both with and against the flow of rivers, enabled Europeans to push into the interior of Africa (and many parts of Asia as well). Steamboats were soon armed with small cannons, giving rise to the term “gunboat.” In turn, when Europeans began steaming into harbors from Hong Kong to the Congo and demanding territory and trading privileges, the term "gunboat diplomacy" was invented, the quintessential example of which was in the unwilling concession to western contact and trade on the part of Japan, considered below.
In addition, major advances in weapons technology resulted in an overwhelming advantage in the ability of Europeans to inflict violence in the regions they invaded. In the 1860s, the first breech-loading rifles were developed, first seeing widespread use in the Austro-Prussian War of 1866 in which Prussian infantry utterly overwhelmed Austrian soldiers armed with older muskets. Breech-loaders were incredibly accurate and quick to reload compared to earlier muzzle-loading firearms. A European soldier armed with a modern rifle could fire accurately up to almost half a mile away in any weather, while the inhabitants of Africa and Asia were armed either with older firearms or hand weapons. Likewise, the first machine gun, the Maxim Gun, was invented in the 1880s. For a few decades, Europeans (and Americans) had a monopoly on this technology, and for that relatively brief period the advantage was decisive in numerous conquests. Smug British soldiers invented a saying that summarized that superiority: “whatever happens, we have got, the Maxim Gun, and they have not…”