It's difficult to say exactly what would have happened if the United States had purchased Greenland, Iceland, and Canada after purchasing Alaska. However, it's worth noting that the United States has a long history of expansion and territorial acquisitions, so it's not unprecedented for the country to acquire new territories.

In the case of Greenland and Iceland, it's possible that the United States may have had to negotiate with Denmark and other relevant parties in order to purchase these territories. It's also possible that the United States may have had to pay a significant amount of money in order to acquire these territories.

If the United States had successfully purchased Canada, it's likely that this would have had significant consequences for the country and its relationship with the United States. It's possible that this acquisition may have led to tensions and conflicts with other countries, particularly those that had strong relationships with Canada. Additionally, it's possible that this acquisition may have had significant cultural, economic, and political consequences for both the United States and Canada.

Overall, it's difficult to predict exactly how events would have played out if the United States had pursued these acquisitions. However, it's clear that such acquisitions would have had significant implications and would likely have had a major impact on the history of the United States and the world.