We can regard the Old Kingdom of Egypt, the cities of Sumerian Mesopotamia, and the Harappan civilization of India as more or less neolithic civilizations. Although they reached great heights of organization and developed complex and sophisticated cultures, they did not progress technologically to any great degree. Their tools remained largely tipped with stone, and agriculture was pursued with wooden spades for plowing and wooden sickles for harvest. They remained restricted to the river valleys where irrigation was a simple matter of digging a ditch and where Spring floods brought fresh layers of silt that maintained the fertility of the soil. As population slowly increased, warfare between city-states for land became common, and successful leaders managed to consolidate several city states into small empires. From time to time, nomadic peoples from the surrounding hills and mountains would attack, attracted by the relative riches of the civilized areas. For the most part, such invaders did not last long. They were either driven off or, being relatively few in number, were absorbed into the much larger population they had conquered. In any case, their culture and technology were not superior to that of these neolithic empires, and they contributed little to their further development.
This situation began to change sometime about 2000 B.C. We are not sure how this occurred or how the necessary technology was developed, but the agriculture of the neolithic empires began to spread from the river valleys and dependence upon irrigation to the hills, where farming soils watered only by rain began to flourish. Smaller civilizations began to emerge around the great centers, deriving their cultural inspiration from their older and more populous neighbors. The Hittites in what is now the nation of Turkey eventually grew into one of the great empires of the Middle East, while the Canaanites in Palestine developed the land that the nomadic Hebrews would eventually claim as their own. There were other such city-states and kingdoms, and many of them developed a lively commerce, acting as middle-men between their wealthy neighbors and the raw materials of the vast spaces of the North. It may well be that similar derivative civilizations arose near Egypt and the Indus Rivers, but little archaeological evidence has yet been found to prove or disprove that possibility.
This slow growth and expansion changed radically in about 1700 B.C. A group of people called the Hyksos invaded Egypt and ruled its richest part until they were expelled after about a century. At the same time, the Kassites invaded Mesopotamia, the Achaeans took over the peninsula of Greece from its original inhabitants, and a people calling themselves Aryans destroyed the cities of the Indus Valley and ruled the region. Still other peoples, called by various names -- Cimmerians, Celts, Galatae -- made their way into the great European peninsula, almost entirely displacing the area's original inhabitants. Still another group, the Gutae, may have swept across North Africa to reach the Atlantic in what is now Morocco. There is still a great argument whether the Tocharians may not have been another group of such invaders, settling on the western borders of China.
All of these groups shared certain similarities. Perhaps the most important was that they used bronze and implements. Peoples in the area of the Caspian Sea appear to have been developing bronze since about 2000 B.C., but the invaders had developed bronze fittings to build two-wheeled chariots, with light spoked wheels, from which they waged war, and pursued horse- raising to provide themselves with the animals to pull their vehicles. Wherever they appeared, they were associated with horses, chariots, and conquest.
Bronze is an alloy of copper and tin. Copper is not exactly rare, but it is not very evenly distributed over the face of the Earth and deposits lie a long distance from some people. Besides, it combines readily with some other substances, such as sulfur, and it requires a great deal of fuel to turn copper ore into usable metal. Tin, for its part, tends to be both rare and even more unevenly distributed than copper. So one must be able to collect copper and tin, along with plenty of wood and workers who are trained in a rather complicated and delicate, and sometimes dangerous, pursuit. The result of this sort of effort was bronze, a lighter metal than copper alone, but one that is much harder. Like copper, however, it is also malleable, and can be beaten out into thin but hard sheets, or into finely carved implements that do not easily wear out in use, or into knives and swords with sharp and durable edges. It can be polished to fine and brilliant shine, and, for all of these reasons and more, is still in use today for both utilitarian and ornamental purposes such as nails, faucets, chains, and belt-buckles. We call it brass.
It was perhaps easier for the peoples of the great Eurasian plain, with its long rivers and broad open stretches, to do this since travel and commerce were much easier than in the zone of civilizations to the south, and easily transported trade goods -- cattle, sheep, horses, furs, and the like -- were more available to them. Whatever the reason, these "less advanced" peoples were the first to develop bronze, and they put it to use long before their civilized neighbors. We have noted one of these uses, the construction of light and tough horse-drawn chariots that became the dominant battle-field weapon and remained so for hundreds of years. The warriors of these peoples went into battle armed with bow and arrow, or sword and javelin, cutting down the people who stood against them while their war-horses trampled anyone whom their masters missed. Some such chariots were equipped with long, curved bronze blades attached to the hubs of the wheels. These would whirl about like a lawn mower as they went against the enemy, and literally mow them down like grass. Sometimes the warrior would guide his horses himself, but more often he was accompanied by a companion who did the driving.
This was a very effective but extremely expensive weapon, and no people could equipped also of their fighting men in such a fashion or allow them to spend their entire lives training for a form of fighting that required an extraordinary amount of dexterity and coordination. So bronze and chariots were aristocratizing innovations. The warrior was the chief of a tribe or a city-state and perhaps had a few nobles who could furnish themselves with chariots and fight for him. Most of the people were peasants who worked to enrich their chief and some of whom went with him to war as footmen to protect him from being overwhelmed by commoners like themselves. I battle, the noble warriors would usually seek out the enemy nobles and fight on foot. If this society sounds familiar to you, it is because it was the society of the Iliad, Homer's epic poem about the Achaean siege and capture of the city of Troy, and the great Indian poem of the Bhagavad Gita. The age of the Bronze Age warriors is what we sometimes call a heroic age and its remains are ancient palaces, elaborate tombs (although not of the magnitude of the pyramids of Egypt), finely worked gold jewelry, and epic poems of battle.
Although the Hittites are fell less well known that the Greeks, Egyptians, or even the Canaanites, considerable work is being done on them, particularly at the University of Chicago (Indiana Jones' school), and a much better picture of them is beginning to emerge. One might start the study of this people with The Hittite Home Page, but HATTI - Homeland of the Hittites is also an excellent site.
Finally, the chariot peoples probably had their most lasting effect in India, where they set many of the basic patterns of Indian life and belief, patterns that remain firm and powerful even to the present day.