In my opinion, the most important primary characteristic of an Ancient State is urbanization. The location of a settlement is key to the future success of the state. The ideal metropolis would be close enough to a body of water that trade would be enabled, but far enough inland so that if an invasion was to take place, it would not be a surprise. A perfect example of this strategic planning can be seen in Ancient Egypt: the Nile River provided a trading route from upper to lower Egypt – in fact it still does to this day – and the proximity to the Mediterranean Sea was an excellent choice to create trade routes between Egypt, Italy, Greece, the area that would become the Ottoman Empire, western Africa and Southwestern Europe.
In addition to having unrestricted access to trade routes, a successful state would be centered in an area where it would be the actual center of a larger governing body. Its peripheral centers would have to be proficient in self managing for the most part, but be close enough to the core to ensure that the core still had control over them all the time.
A large population is essential for an urban metropolis to succeed. Obviously, an ancient state does not pop up overnight with a population of 100,000 people. It usually started out as a sedentary community made up of a group or several groups of hunter gatherers-turned farmers. The area would amass more and more people as time went on, by which time the settlers would have begun to build actual houses instead of tents and/or temporary living arrangements. Fields would have been planted for permanent food supply, some sort of irrigation would have been constructed, and more and more people would migrate to the area to settle down. Soon, the area would have been in need of more space for the growing number of people wanting to live there, and periphery communities would have been established. These would generally have their own leader, who would report to the central figurehead back in the core city. Once the city got to be a certain size, it would have most likely been involved in some type of warfare with neighboring cities. Because of this, there would have been a need for an army of sorts, made up of people who could defend the city and perform attacks on invaders if necessary.
Overall, an ancient state had no chance of survival if it did not have a strategic location that would be beneficial in regards to trade, a growing population, and a need for a strong defense team to keep the city from collapsing