While the Mayans, Olmecs, Incas, and Aztecs are all ancient Mesoamerican civilizations, they were all very different and distinct in their cultures, lifestyles, and accomplishments. Much of this had to do with the geography, climate, and resources of the areas in which they inhabited as well as the interactions they...
were able to have with other cultures during the times they existed.
The earliest of these civilizations were the Mayans (from approximately 2600 BC). While they were the longest lasting, much of their greatness, including their largest cities, resulted in their ability to piggyback off the achievements of the Olmec, who came later (around 1400 BC) and constituted the first major Mesoamerican culture.
The Olmecs, unlike the other civilizations, were not builders and created no major cities (they created one pyramid in 1,000 years), which may be one of the reasons why they are not as widely remembered as the other civilizations. But their innovations in math, science, astronomy, farming, art, and hieroglyphic writing influenced other civilizations either directly (the Mayans) or indirectly (the Aztecs).
The Incas emerged about 1,600 years after the Olmecs disappeared (around 1200 AD) and lived in the highlands of South America (what is now Peru). Unlike their lowland predecessors—the Mayans and Olmecs—the Incas engaged in terrace farming and used irrigation systems that were part and parcel to mountain living. Unlike the Mayans and Aztecs, they also built intricate road systems that were necessary for the travel in their region.
The Aztecs came about much later (approximately 1300 AD) in what is now Southern Mexico. They were explorers and conquerors, and while they lacked many of the Incan advancements, they could write and had a yearly calendar. The Incas had no written language.
The cultural fates of the Incas and Aztecs were also more heavily shaped by the outside influence of the Spanish. The Incas lasted only about 300 years before being colonized and eventually wiped out by the Spanish, largely because of an Incan civil war at the time that left them exposed and fractured. Similarly, Spanish invaders took over the Aztec empire and eventually led to their decline around the same time as the Incas. However, the Mayans and Olmecs simply faded away over time, for reasons that are still not completely known.
North American Indians are a different sort altogether, as it's believed they came to the North American region across the Bering land bridge or by boat at least 15,000 years ago. Their culture emerged quite separately from Mesoamerican cultures to the south, and unlike the other cultures, it still exists today where accounts of their past have been passed down through generations and can still be recounted in person.
North American Indians themselves are a broad group and cover many different tribes, each evolving in many different ways depending on the climate, topography, and other factors of their region. Some were fierce hunters, others more agricultural. Many developed hieroglyphics and calendars, but none built pyramids the way their Mesoamerican counterparts did. Some lived in highlands, others lowland plains. In fact, just the differences between individual tribes are as different as those between Mesoamerican cultures.