I checked your other link, no where does it say that the UN plans to "replace American population with 600 million South American Migrants" far from it, and so very far from the truth. You criticize ones for not reading your links and yet neither do you read your own links! And by not reading your own links you end up giving false witness, telling lies.
This is what it actually says:
United Nations Population Division, Replacement Migration 77
8. United States of America
(a) Past trends
The total fertility rate in the United States dropped from 3.45 births per woman in 1950-1955 to 2.02 in 1970-1975. Except for a temporary period during the late 1970s and early 1980s, when it hovered around 1.8, the total fertility rate has continued to be around two children per woman. Life expectancy at birth, meanwhile, has risen from 69.0 years in 1950-1955 to 75.7 years in 1990-1995. As a consequence of these changes, the proportion of the population aged 65 or older rose from 8.3 per cent in 1950 to 12.5 per cent in 1995, and the potential support ratio declined from 7.8 in 1950 to 5.2 in 1995. As a point of comparison, the potential support ratio was 15 in 1900, when 4 per cent of the population was aged 65 years or older.
(b) Scenario I
Scenario I, the medium variant of the United Nations 1998 Revision, assumes an annual net intake of 760,000 migrants per year between 1995-2050, for a total of 41,800,000 net migrants during the period. Accordingly, the total population of the United States is projected to increase continuously from 267 million in 1995 to 349 million in 2050 (the results of the 1998 United Nations projections are shown in the annex tables). By 2050, out of this total population of 349 million, 59 million, or 16.8 per cent, would be post-1995 immigrants or their descendants. The population aged 15-64 would increase slowly from 174 million in 1995 to 214 million in 2050, although not in a monotonic fashion. The population aged 65 or older would rise rapidly, from 33 million in 1995 to nearly 76 million in 2050. As a result, the potential support ratio would decrease from 5.2 in 1995 to 2.8 in 2050.
(c) Scenario II
Scenario II, which is the medium variant with zero migration, uses the fertility and mortality assumptions of the medium variant of the 1998 Revision, but without any migration to the United States after 1995. The results in this scenario are quite different from those of scenario I. The total population would increase to 290 million in 2050, which is 50 million less than in scenario I. The population aged 15-64 would rise from 174 million in 1995 to 192 million in 2010 and 2015 and then decline, returning to 174 million in 2050. The population aged 65 or older would double, from 33 million in 1950 to 68 million in 2050. As a result, the potential support ratio would decline to 2.6 in 2050, which is slightly below that presented in scenario I.
(d) Scenario III
Scenario III keeps the size of the total United States population constant at its maximum of 298 million, which it would reach in 2030 (assuming no in-migration after 1995). In order to keep the total population constant at that level, it would be necessary to have 6.4 million migrants between 2030 and 2050, which is an average of 319,000 migrants per year. By 2050, out of a total population of 298 million, 7.3 million, or 2.5 per cent, would be post-1995 immigrants or their descendants.
(e) Scenario IV
Scenario IV keeps the size of the population aged 15 to 64 constant at its maximum of 192.5 million, which it would reach in 2015 (assuming no in-migration after 1995). In order to keep the working-age population constant at that level, 18.0 million migrants would be needed between 2015 and 2050, which is an average of 513 thousand migrants per year. By 2050, out of a total population of 316 million, 25.0 million, or 7.9 per cent, would be post-1995 immigrants or their descendants. 78 United Nations Population Division, Replacement Migration
(f) Scenario V
Scenario V does not allow the potential support ratio to decrease below the value of 3.0. In order to achieve this, no immigrants would be needed until 2025, and 44.9 million immigrants would be needed between 2025 and 2035, an average of 4.5 million per year during that period. By 2050, out of a total population of 352 million, 61 million, or 17 per cent, would be post-1995 immigrants or their descendants.
(g) Scenario VI
Scenario VI keeps the potential support ratio at its 1995 value of 5.2 persons aged 15-64 for each person aged 65 or older. In order to keep the potential support ratio constant at that level, it would be necessary to have 593 million immigrants from 1995 to 2050, an average of 10.8 million per year. By 2050, out of a United States total population of 1.1 billion, 775 million, or 73 per cent, would be post1995 immigrants or their descendants.
(h) Additional considerations
The official United States estimate of (documented) migrants into the United States from 1990 to 1996 is about 1.1 million per year. Thus, the past regular inflow into the United States is well above the number of migrants needed to prevent a decline in the total population or in the working-age population. Also under both scenarios III and IV, the percentage of post-1995 immigrants and their descendants in the total population of 2050 (2.5 per cent for scenario III and 7.9 per cent for scenario IV) would be below the percentage of foreign-born that exists currently (9.6 per cent). Figure 23 shows, for scenarios I, II, III and IV, the population of the United States in 2050, indicating the share that consists of post-1995 migrants and their descendants.
In the absence of migration, the figures show that it would be necessary to raise the upper limit of the working-age to 66.9 years to obtain a potential support ratio of 3.0 in 2050, and to about 74 years in order to obtain in 2050 the same potential support ratio observed in 1995 in the United States, which was 5.2
persons of working age per each older person past working age. Increasing the activity rates of the population, if it were possible, would only be a partial palliative to the decline in the support ratio due to ageing. If the activity rates of all men and women aged 25 to 64 were to increase to 100 per cent by 2050,
this would make up for only 21 per cent of the loss in the active support ratio resulting from the ageing of the population.