Flags are interesting, they are a simple graphical device that represent a whole nation. Naturally, flags become entwined with a nation's global reputation and cultural influence so that they are symbols, icons, brands, and logos all at once. This is powerfully demonstrated when angry mobs burn a flag as a gesture of anger toward a nation, or when a popular uprising replaces a flag to indicate the end of one regime and the start of a new one. Similarly, when one nation defeats another, often raising the victor's flag is the chosen gesture to indicate military conquest.
As they stand, however, flags are not perfect. The Italian flag, for example, is in clear contravention of good visual design principles. Because of the poor use of red and green, 10% of men who are red/green colorblind might accidentally book a flight to Italy instead of Nigeria. Flags also lack any sense of history, with the exception that the older more established countries get to choose good designs while the latecomers get the leftovers*. I propose an improved system to make the flag something of a "living" symbol.
So, to encode history I suggest that major events be included in the color and pattern of the flag. An instance of a major event would be the conquest of one nation- state by another. To demonstrate, I'll work through a couple of examples. Take the UK, the bulk of the land mass has been successfully conquered by Vikings and Normans, while there might be arguments about whether the Normans were French or in fact just a sort of Viking franchise, the outcome is the same. The British flag must incorporate red, white and blue as derived from the Norwegian&Danish/French flags. This is just fine and no changes are required to the Union Jack.
The French flag is different, multiple successful invasions by Britain would mandate the inclusion of red, white, and blue into the flag, obviously no change there. However, some change is mandated, so I propose that color is followed by shape change, so the French flag should incorporate cross motifs. France has also been invaded by Germany and the USA, consequently, those features should also be included. The resulting French flag would be a sort of muddled stripey brown tartan. Belgium and Italy would show subtle differences but an overwhelmingly similar brown tartan theme reflecting their shared history. Scotland would have to incorporate a red cross to reflect English victories, it might look a lot like this [link].
Such a system might foster robust national defense, or perhaps discourage the sort of activities that force international coalitions to invade.
* possible mitigation for the Italian debacle.-- bs0u0155, Jan 16 2019 Proposed Scotland Flag https://en.wikipedia.org/wiki/Union_Jack [bs0u0155, Jan 16 2019] Sounds a bit like heraldic coats of arms.-- 8th of 7, Jan 17 2019 random, halfbakery