This submission has been removed because it violates the rule on poll-type questions. These poll-type questions do not lend themselves to answers with a firm foundation in sources and research, and the resulting threads usually turn into monsters with enormous speculation and little focussed discussion. “Most”, “least”, "best" and "worst" questions usually lead to vague, subjective, and speculative answers.

For questions of these types, we ask that you redirect them to more appropriate subreddits, such as /r/history or /r/askhistory.

And since it's Friday you could also ask in the Friday Free for All thread.

An easy one might be the dropping of the atomic bombs on Hiroshima and Nagasaki. They were industrial but nonmilitary targets with a horrendous civilian casualty rate, but the act prevented an even greater loss of life from the alternative plan of a full scale invasion of Japan with casualties projected to exceed 100,000.

The sale of Alaska to the USA was deemed controversial by both sides at the time.

The Argentinian claim of the Falklands in rather recent, and thus, probably the easiest to research.

The League of Nations refusing to intervene when Mussolini invaded Somalia.

Now, if you want more controversial topics that have a bit more coverage due to conspiracy theorists, might I suggest the following topics to look into:

• Roswell

• Is Fort Know empty?

• Kennedy Assassination

• The Treasury Act

• 9/11

• Moon landing.

I want to make it known that I do not believe in most conspiracies, I just find them incredibly interesting.