The Holocaust is fulfillment of totally different prophecy than the Great Tribulation where God ended the first covenant with great violence and wrath.
16 And the ten horns which thou sawest, and the beast, these shall hate the harlot, and shall make her desolate and naked, and shall eat her flesh, and shall burn her utterly with fire. Rev 17
...i.e., the curses of Lev 26 & Dt 28 laid upon the Jews over the past two millennia. Not a doubt in my mind Hitler was the personification of one of those 'ten horns'.
So why choose the holocaust? Remember that the "Great Tribulation" is against the nations of the world, and is the salvation of the world not the extermination of Israel. You have these events confused.
Why not choose the Asian Genocide instead?
The Asian Holocaust was perpetrated by Japanese Emperor Hirohito and the Imperial Japanese Army during World War II.
Estimated killed: 10,000,000
Or perhaps The Holodomor (1932-1933)?
The Holodomor was the extermination of Ukrainians by famine. It was perpetrated by the Soviet Union under Joseph Stalin.
Estimated killed: 7,500,000
Or, The Congo “Free” State (1885-1908) ?
The privately owned “Congo Free State” was controlled by Leopold II of Belgium. It is said that during his control of the region he committed numerous crimes against humanity upon the indigenous Africans of Central Africa.
Estimated killed: 10,000,000
http://www.rantpolitical.com/2014/12/06/15-worst-genocides-in-history/
Why just the Holocaust you term as a "Second Tribulation"?
Any one of these genocides could have been a "fulfillment of scripture" in your scheme of things. But none of them, not even the holocaust, fulfills the scripture that you quoted nor the other related prophetic scriptures.