Writing this on my phone, so sorry for any formatting issues.

So Ancient Economies is actually its own subject within the study of Ancient History.

First off, when considering the financial systems of these different empires, they all would have had their own, though they did interact on a grand scale.

It also depends on what time period you are talking about. As things did change over the course of thousands of years and can be substantially different depending on the era and civilizations.

Our oldest financial documents are also our first documents in history. They originate in in Sumer around 3300 BCE. The original were very basic in their designs that started off as clay pieces that represented an amount that later became markings that would lead to the cuneiform writing system.

These documents are mostly receipts, inventories and ledgers. There are actually more documents from the time of the Ur III period (around 100 years) than the entirety of the Roman period.

The Mesopotamians including Sumer, Babylon and Akkad were all heavy documenters especially when it came to trade and commerce. We actually know a lot on how their economy worked and we are still learning more as there are thousands of clay tablets and fragments still to be translated.

When it comes to the connections between these empires we can see their interactions throughout different periods.

One of the most known is during the end of the 2nd millennia known as the Amarna period. It was a time during the Late Bronze Age where we have clear documentation on the relationship between the kings of these empires. Bases on letters found in the archives of Amarna (The City Akhenaten and Nefertiti founded and made the capital of Egypt but was abandoned after Akhenaten died).

These letters are between kings and discuss their relationships, stating how they went back generations and existed between their fathers. They also discuss the trade of highly valued items that only a king could have to trade in such high qualities like gold from Egypt, Copper from Crete, Tin from Anatolia and Lapis Lazuli from Afghanistan. These letters give us an in depth of the relationships between kings and kings and their vassals over a thirty year period.

The letters were also in Akkadian, as that was the language used for all official documents. Showing that they did indeed have a system in place for for trade and communication on a large scale.

They all had intricate governments with scribes and administrators for everything.

Though at the end of the Late Bronze Age there was a system collapse that ended the large scale communication and trade between these civilizations. Though it still existed in minor forms and would later form again in the classical period.

When it came to loans, it’s important to understand that most Free laborers were in a perpetual system of debt. This was because, they often did not have savings, so to buy anything for everyday use or for farming, they’d often have to take out a loan. You could get a loan from another free laborer, merchant, or land owner. Many of these loans were outrageous, and people often had more than one. Now if a person could not pay their loans, they or their family could be taken as slaves to pay off their debt. It is important to note that slavery was not a permanent position and was one that a person could be in during different times throughout their life. Debt bondage was a common part of ancient life, especially for the day laborers.

In some places like Mesopotamia, every so many years the King would forgive all debts. Because in some instances, large portions of their free labor force would be bond slaves and could not complete their corvee labor ( a type of labor each free person in a community had to do, it was like paying your taxes through farming or building temples for the state).

“A History of the Ancient Near East” - Marc Van De Mieroop

“The Amarna Letters” - William L Moran