I have made a fairly simple time machine. It works by ... well that's not important. It can send one user back in time (up to two hundred years). This person can appear anywhere they want on this planet, carrying what ever they physically can, but can only stay there for two minutes before getting shot forward in time (to the present day, once again any place they choose). (They cannot cease to exist through this action, because ... well that's not important either, just trust me...)
My question is thus: What is the smallest change one could make within the past two hundred years to save the most lives? Remember it has to be accomplished within two minutes. Also you are unable to leave anything behind, only the changes you have made, and the memory of you (where applicable) will stay behind.
Please hurry, I have much to do and so little time...
EDIT
Addendum: It was only a matter of time before it would happen. There were plenty of signs we missed. We were foolish.
Luckily, their coming coincided with the day I completed my machine. A work fifteen years in progress... We held off stage two testing it until we had a plan.
Finally, after months of horror, squad 7 captured one of them. Over a hundred men died that day...
The captive was rushed to our last refuge... An old mine well hidden so that we could stand a chance... Twenty of the worlds brightest [admittedly, not such a great feat anymore] waited here. Waiting for this very day. One had never been captured before...
But alas, it was a trap. Fire rained from the roof as our last hope crumbled. Without exception, their presence indicates death. Our weapons are more useless against them than...than... oh bother...
My machine will allow me one chance (this time) to travel back to make a change. On the topics of weapons I know next to nothing. I have 120 seconds so I must do an action as I do not have enough time to convince anyone of the impending doom. My only hope, the morbid thought that keeps me going is that if I can save enough lives we can last for longer this time. Time we need to formulate a plan.
We have concluded that lives == time. Therefore Stage one of my plot is to save as many lives as I can. The more people we have when they come, the longer it will take for them to get to us.
Whether in this revision or the next we will come up with a plan. We just need time; and for that we need people...