The correct answer is - taxes.
After the civilizations started to establish themselves and prospered, they needed to secure their citizens, and that was only possible if they had a strong military that will keep any intruders out of their territory.
The military is not cheap, and it needs a lot of funds, as it constantly needs food, clothing, armor, weapons, training, and all of that had to be sponsored by the governments/rulers. In order to be able to have strong and happy military forces, the governments started to tax the people, and initially that was only to sustain the military, but over time developed much more and is used for lots of other things nowadays.
Railroad tracks and total population is most likely the correct choice.
Answer:Solon contributed to Athenian democracy by outlawing debt slavery and proposing that all citizens could bring charges against another and participate in the assembly. Cleisthenes allowed all citizens to submit and debate resolutions, weakened the power of the nobility, and established the council of five hundred.
Explanation: I Hope I helped
Mesopotamia's rivers (Tigris and Euphrates) are key to their civilization.
Because of the rivers Sumerians (Mesopotamia's people) could trade and travel through them.
Not to mention just plain drinking water.
Another benefit of the rivers was irrigation.
