What caused this demographic switch ?

The argument is that the mortality transition occurs exogenously and is the cause of a subsequent decline in fertility and rise in urbanization. This exogenous demographic process plays out over time, and has effects on economic, social, and political development. Hope this helps. :)

since most of current immigration into the u.s., both legal and illegal, is coming from latin america. it would be very difficult to imagine or rationalize a country my fellow citizens are trying desperately to flee into, would pose a threat to my prosperity or freedom. since the u.s. has a long history of intervention, but no record of permanent occupation, i would not feel oppression is the main objective.  

the largest free trade nation, along with the largest gdp in the world wanting to expand it's economic policy on us, and including us, could only be positive. the u.s. government has no interest in, or way of simply forcing american culture on us. and has no track record of it. other nations that adopted american social culture, or "americanization" did so voluntarily, mainly through the choice of allowing american businesses and u.s. citizens to come into their nations, as free operatives.

the two things that develop a strong social foundation are: a. separation of church and states e. education received attention separation of church and states separate the illogical  argument that came from religious beliefs to a fact based belief. while education will make us remember the past to avoid the repeat of our mistakes.