Firstly, Adolf saw (like some people today still do) Capitalism and Communism (see: Jewish Bolshevism) as products of a Jewish conspiracy.

Secondly, he was a soldier in the Bavarian Army. Let's say he was a bit of a sore loser, considering the utter destruction of the German economy, death of his fellow countrymen, etc etc. (Germany was effectively saddled with the cost of the war. As in, ALL OF IT)

So, simply put, old Adolf saw it as the Jew's fault for Germany's troubles.

Add that to a great iteration skill, conflicts back home (Communists and other political parties vying for control), a severe depression (as Jonathan Steinberg puts it, "A woman left a basket of 60 million Reichmarks on the ground, and came back to find the basket had been stolen, but the currency was dropped about on the street...") which lead to LOTS of angry poor people, and you've got good breeding ground for a nationalistic, hate-filled society willing to follow the guy who promised to bring them OUT of said depression, and do what he commands.

And what did he command? The death of the Jews.

I hope I helped! I'd suggest reading Mein Kampf if you have the time. It's free on .pdf and gives a good insight on the mind of a madman.