I know very little about the pre-colonial Americas, unfortunately, but I'm aware that a large number of pyramids and ziggurat-like-structures were constructed by various civilisations. Would these pyramids usually be situated in the midst of cities? Where was the manpower for their creation sourced - obviously, large numbers of skilled craftsmen would have been required alongside manual labourers. Finally, were these pyramids invariably religious in purpose, or would they serve other purposes such as palaces or forts?
I realise this is a sweeping generalisation of numerous different cultural groups and with no set time-period. Apologies for that - I honestly know so little about pre-colonial America that it's hard to give any specific details.
That is quite a broad topic indeed, so I am going to focus on the one region and system I am most familiar with although I could expand on the topic and talk about Hawaii, the American Southwest, and Chan Chan.
Within the Maya region, Elliot Abrams has argued that Classic Maya rulers made use of a labor tax system in order to construct their monumental architecture. In order to prove this, Abrams conducted an architectural energetics analysis of the largest building at the site of Copan, Structure 10L-22. Architectural energetics is the quantification of materials and labor that went into constructing a building. Different building material volumes are estimated based on excavations. Those volumes are then used in formulas for known rates of work that come from replicative experiments. These formulas produce person-days or person-hours depending on the activity. Adding together all these different person-days and person-hours gives you a total amount of labor that went into a structure.
In Copan's case, it took 30,498.6 person-days to procure the materials, transport them, manufacture some materials, and construct the building. For Abrams' work he assumed that 10L-22 was constructed in a single build phase despite excavations showing that the structure was built over several build seasons with each season expanding on the previous construction like layers of an onion.
If 10L-22 was built in a single phase, you need determine how much time you want to devote to construction. Abrams chose the dry season as the time period for construction because the lack of rain would aid in keeping the building stable until its protective outer surface was constructed. A dry season at Copan lasts roughly 120 days. Abrams, being conservative, decided to go with a 60 day build season to allow for the people of Copan to take care of necessary activities before and after construction. Taking the total number of person-days estimated from before and dividing it by 60 days, gives us the number of people needed to construct 10L-22. That number is 508.
But to make it more realistic, Abrams split the total number of person-days into unspecialized and specialized labor to give a more accurate estimation. The total number of unspecialized labor person-days is 22,244 which requires only 371 people to work 60 days. The total for specialized labor was 8,229 person-days which requires 40 people over 60 days. Based on his estimations, 10L-22 only needed 411 people roughly two months to build. Expanding the construction time only reduces the number of laborers required. And changing the estimates of the person-days required, which are already rather conservative and give a lot of leeway in terms of skill and work day, doesn't really affect the entire estimation all that much.
How does 411 people working on one project affect Copan's ability to provide labor? Well, there isn't much of a drain. The estimated population of Copan in the Late Classic was 15,000 people with a potential labor pool of 3,000 to 5,000 adult males. 411 people is but a tiny fraction. A labor tax system makes some sense for Copan. A family head would only have to contribute labor two or three times their entire life which isn't bad all things considered.
But this is Copan, just one example that cannot be universally applied across the entirety of two continents.
Abrams, Elliot Marc. Systems of labor organization in the late classic Copan, Honduras: the energetics of construction. Diss. Pennsylvania State University, 1984.
Abrams, Elliot M. "Economic specialization and construction personnel in Classic period Copan, Honduras." American Antiquity (1987): 485-499.
Abrams, Elliot M. "Architecture and energy: An evolutionary perspective." Archaeological method and theory (1989): 47-87.
Abrams, Elliot M., and Thomas W. Bolland. "Architectural energetics, ancient monuments, and operations management." Journal of Archaeological Method and Theory 6.4 (1999): 263-291.