I would create an underwater tidal turbine system that connected all the continents that generated additional global power from the biggest substance on the planet. Then at the connecting points, de-salination plants to turn salt water into fresh water to ease any water shortages. Provide education and irrigation in third world countries to allow people to be self sufficient. I would engage each nation to accept their own and their neighbouring countrymen through further education and peaceful communications. Also I would invent and create an Apathy Magnet and suck all the indifference out of the world.