From the history videos I’ve watched so far it seems like every continent had at least one major civilization form (South/Central America, Europe, Asia, Africa). How come there wasn’t one in North America?

The videos you are watching are evidently not giving you a clear perspective on this question, because there were native chiefdoms, cities (boasting residents estimated in the tens of thousands) and monumental architecture (e.g. stone and adobe constructed towns, temple mounds, burial mounds, and earthen pyramids) in North America north of Mexico. You should look into the Mississippian Period cultures in the eastern woodlands and the Ancestral Puebloan cultures of the desert southwest. This question has been addressed in a number of posts that can be found in the FAQs for this site. Please look to the posts by /u/Reedstilt, /u/RioAbajo, and /u/Cozijo here, here, here, and here for discussions of prehistoric population and cultural complexity as well as links to reconstructions of urban centers. Now I don't want to discourage further discussion, but these posts will definitely give you a place to start.

In this post scroll down just a little and you will find a number of resources for your reading peasure provided by /u/Reedstilt.

Edit: With regard to your second question about differing population densities in North and South America, you should know that population estimates in the prehistoric period are very speculative and New World anthropologists have been arguing about them for years. So don't put a great deal of stock in generalizations about Pre-Columbian population densities. In addition, North America north of Mexico boasted a number of locales like the California coastal region that boasted very high population densities when compared to other prehistoric New World groups.

I'm mainly commenting here so that if anyone have any follow-up questions, I can tackle those - since some of my older posts have already been linked here.

But while I'm here, I figure I should mention that the Aztecs, Olmecs, and most of the Maya are technically North American. Central America begins south of Mexico, and I know mislabeling that can be a bit of a pet peeve for our Mesoamerican specialists around here. I'm assuming by "North America," you're referring to north-of-Mexico North America, or what is today Anglo-America (as opposed to Latin America). In other words, the United States and Canada.

Is there any trace/information about pre-colonized North America?

Winter Counts - an indigenous form of history-keeping using pictograms- on the Great Plains go back to around 900 CE, beginning with Ptesáŋwiŋ (also known as White Buffalo Calf Woman) founding the modern Lakota religion. Unfortunately no Winter Count itself is actually that old, so they're all copies of copies of copies, and for the ones that actually go back that far, the remote past is recorded in less detail than more contemporary history.

Other societies had similar methods to record their histories, whether its the birchbark scrolls of the Ojibwe or the Calendar Sticks of the Powhatan.

Did they have forms of writing?

There is one potential pre-Columbian writing system in the region, but colonialism has muddled the situation here. Mi'kmaq hieroglyphics used, in some fashion, prior to 1675, but we don't know much about them back then or how well developed they were as a true writing system. After 1675, Le Clercq - a French missionary in eastern Canada - altered and added to the pre-existing system to make the writing system as we know it today.

I know they did trade art with other peoples but was it more tribe to tribe or did they know of the Central/South American empires?

We have virtually no evidence of direct interaction between people from eastern North America and those from Mesoamerica. One grave site at Spiro (a Mississippian community) has a small piece of obsidian that came from Mesoamerica. That's the only artifact that links to the regions. The oral histories of the Natchez from Louisiana contains a somewhat ambiguous narrative concerning the "Ancients of the Land" (a generic term for Native peoples living to the west or southwest of them, across the arid regions of Texas). This narrative echoes the downfall of the Aztecs to the Spanish, but whether they got this information directly from Mesoamerican sources or from the Spanish they took captive following de Soto's failed attempt to conquer the American Southeast is unknown.

For people in the American Southwest, the story is a bit different. For years, it seemed like the Mesoamericans were importing much of their turquoise from the American Southwest, but I've heard some recent studies have called that into question. It might be a good idea to ask a question about that specifically to attract the attention of someone who would be more knowledgeable about that area of archaeology. Even if the turquoise angle isn't as strong as it used to be, we still have sites like Paquime near the US-Mexico border, where people were raising parrots that are native to areas much further south in Mexico. This suggests more direct contact between the two regions than just passing items from one community to the next.

How can I read up more on the americas pre-colonization?

That's a big question. Anything in particular you'd like to know? More generally, an old post of mine with several different books on the archaeology of eastern North America has already been pointed out.

as a follow up question, since it is theorized that the people in the Americas came from Asia, how come there were so many more people in South America than in the north?

The initial migration from Asia is so long ago that it has little baring on the distribution of people at the time of European contact. The migration occurred thousands of years before the last glaciation ended. By 18,000 years ago (at least) people were already well established in southern Chile. By the time the glaciers retreated and the climate started becoming favorable to agriculture and the affair of statebuilding, people were already well distributed all over the Americas.

Agriculture was probably started in four different locations throughout the Americas: The Ohio-Mississippi river valleys, Mesoamerica, the Andes, and the Amazon. The agriculture of the Ohio-Mississippi river valleys, otherwise known as the Eastern Agricultural Complex (EAC) took a bit of a different form than most other agricultural systems developed around the world. It wasn't always as productive as these other systems, though in the right conditions it could be. Where it really shined though is in providing a diverse balance of nutrients.

As iconic as maize/corn is in Native American agriculture, it was actually a relatively late arrive from Mesoamerica. People only started using it as a regular food source around 1000 years ago, which is when we start to see the big Mississippian cities like Cahokia pop up around eastern North America. We also see people suffering from poorer diets around this time as a corn-heavy diet replaced the more nutritional balanced EAC diet. Around 700 years ago though, beans make their way up from Mesoamerica too and help mitigate the nutritional imbalances caused by eating so much corn. Some EAC crops continued to be grown - sunflowers and certain squashes being the most notable - while others got pushed out of the crop fields and into the herb gardens, or were abandoned entirely.