Keroro
Dororo: Ninja Frog
Macedonia in June, 323 BCE. My generals would be loyal to me, right? 

I noticed that no one chose Napoleon durin the 1800s, If I was him, I would capture spain, britain, italy, austria-hungary, prussia, and possibly the ottomans (Not Russia, the cold winds will destroy my troops, Napoleon shoulda realized dat)
About the question... Assuming I knew what would come, I would take Portugal 1481, get the iberian union right, make sure Columbus never returned to Spain (gaining some time), and start settling North America instead of spending resources going for Asia or in the jungles of South America. Of course, no one then could guess the coal and iron of North America would, centuries later, become more valuable that the spices of Asia...
Great Britain, 1760, stop the revolution and cancel all the bloody taxes
You'd capture Britain, would you. And how would you do all that when Napoleon failed? And why?
Actually, I wouldnt invest in offensive navies, only defensive ones, and conquer as many on lands as possible, create a pact with Russia, and then build up navies, and then go to countries with water between France and the other nations
PS: Nice Arguement u made there inom..- well the guy with a bear for a avatar
EDIT: Ooo and I 4got to say I would create peace with Britain and possibly Spain...until I have command of Italy, Prussia, Austrai-Hungary, and Possibly the Ottomans
by Defensive navy, I meant by makin em patrol my seas