The European Elites, all Leftists, destroyed their own national cultures, destroyed their sovereignty by creating the European Union with open borders and unlimited welfare benefits. They have destroyed themselves by declaring Nationalism to be bad and by creating a nanny state where people shirked work and got as many “freebies” as they could.
The Left in America, headed by Obama, Hillary, Kerry, Biden and Bernie Sanders is trying to do the same thing here. Welfare without Workfare and a refusal to seriously enforce immigration laws have people from not only Mexico but Central and South America and Asia pouring into this country and going directly on the welfare rolls.
And the ideology that supports these Leftist policies is Multiculturalism, the belief that all culture are equal and that different cultures can exist in the same place at the same time without assimilating. Two competing cultures diametrically opposed to each other cannot coexist together peaceably. If the immigrants refuse to assimilate into the host country then they will take over the country and become the majority making the original hosts the minority. This is why the Brexit vote went the way it did. Ask yourself if you would enjoy having your traditions and your culture over run by another culture that you strongly disagree with?