Waitaminnit - what makes you think that any of those events could be "fixed" by a today person, traveling back in time, when we know about all kinds of stuff facing us now - climate change, Capitalism on the rampage, Ebola, AIDS, and Republicans - and we can't fix those things? Hmm

You never change things by fighting the existing reality.
To change something, build a new model that makes the old model obsolete.
R. Buckminster Fuller