The Torah lists four specific animals that are not Kosher. The camel, Shafan, and Arneves whom all chew their cud but do not have split hooves, and the pig who has split hooves but does not chew its cud. The Medrash says that these non-kosher animals represent the four exiles of Yisroel. The first three represent Bavel, Madai, and Yavan, while the pig represents Edom.
The Vilna Gaon explains that all these have one siman tumah and one siman tahara. The first three all chew their cud. They possess the internal siman tahara. However on the outside their hooves are not split. These three kingdoms were great kingdoms with great talents and accomplishments. However their exterior, the application of their talents were tamei. Edom is the opposite. They show a kosher face with their hooves, yet on the inside they are tamei. This is like Eisav himself who fooled his father and the entire world, professing to be a tzaddik but was a corrupt Rasha down to every fiber of his being.
The Vilna Gaon brings the gemara (Yuma 9b) which says that the first Bais HaMikdash was destroyed because although we were tzaddikim, we committed the three terrible aveiros which everyone knew ans saw. Appropriately we became captive to nations that also were great on the inside but criminal in their exterior actions. In the second Bais HaMikdash we looked like tzaddikim on the outside but we were corrupt beneath the surface in the way we related to Hashem and to our fellow man. For this we fell to a nation who possessed the same shiny exterior and rotten inside.
This says the Gra explains the enigmatic gemara that says, "Tova Tzipornan Shel Rishonim" better are the fingernails of the earlier generations, where the sin was outside, "MiKreisam Shel Acharonim", then the bellies of the later generations, who carried a fine exterior but deep in the pit of their stomach they were rotten.
This is the galus of the Chazir that we still live in until today. The advanced Spanish, the enlightened Germans, and all the polite and tolerant nations today, put on a wonderful face. On the inside though the words of the of the Hagada still ring true, Omdim Aleinu LiChaloseinu. Until we learn to be G-d fearing Jews, not just on the surface but also deep down inside, out nation will continue to be held captive and suffer oppression at the hands of those whose evil lurks behind smiling upstanding faces.