What allowed the Europeans to explore further into Africa and eventually conquer more?

During the nineteenth century, Europeans were able to advance into the interior of Africa. Improved military, communications, and transportation technology allowed them to do so, and more effective drugs to fight malaria helped as well.
The specific “tools of imperialism” that facilitated Europe’s colonial conquests in Africa included breech-loading repeating rifles, light field artillery, smokeless gunpowder, iron-hulled steamships, railroads, quinine, and, later, machine guns. The introduction of submarine telegraph cables enabled European colonial authorities to communicate by telegraph; this allowed them to use their limited resources in a more effective way and to send reinforcements where they were badly needed.
Quick-firing British and French rifles and artillery were important in helping British and French forces to conquer parts of Western Africa in the late nineteenth century, and the new Maxim machine guns played a decisive role in the defeat of the large-scale Sudanese Mahdi uprising against the British in the battle of Omdurman (1898). Many thousands of rebels died, but the British and Egyptian forces lost just a few dozen of their own people. The Maxim machine guns devastated the courageous Ndebele warriors in South Africa (1893), thus defeating one of the strongest states that opposed the British colonial advance.
Where European troops did not have an overwhelming technological advantage and African forces were reasonably well-trained in the use of modern weapons, the European invading armies sometimes experienced crushing defeats. The Ethiopian victory over Italian forces in the battle of Adwa (1896) is a notable example of this.