There are a number of common approaches to history which - popular though they are - encourage false assumptions. We call these common fallacies and briefly list three below:

1. apples and oranges - drawing comparisons between events or sets of circumstances that seem to share a common denominator but are in fact distinct from one another by virtue of having occurred during different time periods, in different places, under different socio-economic conditions, to different groups of people, etc., can lead to the incorrect assumption that, just because something is true under one set of circumstances, it will necessarily hold true for all circumstances of a similar sort. The act of making such comparisons is sometimes referred to as "comparing apples and oranges."
2. presentism - thinking about history from an exclusively "presentist" point of view (i.e., from the perspective of our present-day understanding of events) fails to take into account that, at the time in which historical events occurred, those involved did not enjoy the benefit of hindsight that has informed our present perspective. Presentism invites us to dismiss the poor decisions made by previous generations as having been based on their failure to anticipate the long-term consequences of their deeds. Yet to fully understand an historical event, we must view it not only with the benefit of hindsight, but also in the more limited context of its own times.
3. "history repeats itself" - we'll make this clear: history does not repeat itself. Yes, we can discern trends in history and - at best - will attempt to learn from the past in order not to repeat its mistakes. That history repeats itself, however, is simply too broad a claim.

In the section on Cause and Effect, you will find a number of other strategies and assumptions you should avoid when writing and thinking about history; see also Don'ts.