Generally, we can observe a cultural fracture (protestant and anglo-saxon in the North ; catholicism in the South) with a marked linguistic division, but also a socio economic fracture : the north is developed and the south is splitted up and contrasted. 

America has always been a place of immigration : with the American Dream and his soft power, it attracted many people (Ellis Island). Today, the USA are the 1st migratory space of the world, with 80 % of migrants coming from the LDC’s of Latin America (ethnic diversity  + democratic gains + human capital (gateway). 

But the American express a strong patriotism and sometimes the reject of foreigners. Regarding latin american countries, they express an anti-americanism feeling, with an opposition to the liberal economy

Moreover, the illgal migrants are not the only illegals flows : at the border, we can observe traffics of drugs and weapons (war on drugs) and the durability of the grey economy. 

exchanges and level of development asymmetric

Economically, there is a negative trade balance : because of NAFTA, USA didn’t stayed 1st in the market of exportation (after China), but she still is the main actor in exchanges while his partners are dependable. 

But those exchanges generate obviously an increase of the importance of the border : indeed the manufacturing employment decrease in USA, in favor of delocalisation to Mexico (maquiladores), so it generate unemployment. But also the creation of twin cities (accumulation of population on the Mexican side) which generates socials inequalities of development and a strong settlement contrast due to migration.

 - NAFTA (1994) : called into questions nowadays by trump wanted to renegotiate the agreement to put first his America first policy. Goal : the equal dvlpmt of trade between Canada USA and Mexico space, which became a market with 470 millions of inhabitants, which is the 1st powerful USA = pillar of this agreement  (75% canadian exports + 78% mexican exports) → mexico and canada benefit of this growth BUT a strong and disempowering dependence persists.

- Mexico also joined the Mercosur (=UNASUR), so he’s less dependant/ counteract to the US domination.

So we observe that they are trying to resolve the problems of economics, culturals, demographics fractures by integrated countries under organizations. But either they don’t work, whether strongs dependances still exists.