What can a country do with 3 trillion dollars?

We have spent over 3 trillion dollars on the war in Iraq so far.

We have spent over 3 trillion dollars to invade and occupy a country on the other side of the planet in order to gain control of its oilfields. The human cost to us has been over 4 thousand dead, over 30,000 severely injured and countless family tragedies. The human cost to the Iraqi's has been estimated at anywhere from 95,000 dead to over half a billion dead.
If we were to invest 3 trillion dollars in research and development of alternate, sustainable, and clean energy sources.....
Can you imagine?
No more worries about global climate change.
No more worries about mining accidents or oil well blowouts.
No more worries about our ancient energy grid collapsing or being attacked by terrorists.
All of the countries who are powerful players on the world stage just because they have oil (Saudi Arabia, Brazil, Russia, etc) would lose their influence over our government.
Iran would have no justifiable reason to develop nuclear power because our solar technology would make nuclear power obsolete.
We would lead the world in clean energy and become unbelievably wealthy by exporting our technology to the rest of the world.
No more deaths from war over oil.
Wow. Just imagine it.