The Monroe Doctrine illustrated two truths about our (and every other nation's) foreign policy. It started by setting forth principles that were meant to be immutable. And over time, it showed how they can be changed in response to changing circumstances — such critical facts as its political stability, the growth of the economy, and its military readiness.
As long as our country was preoccupied with building up these strengths, the Monroe Doctrine and American foreign policy remained largely the same. But as time went on, the relative strengths of America and the foreign powers underwent a profound change.
To begin with, America became the magnet for millions of people who were brave, restless, and hardy enough to hazard the long and dangerous journey to what was seen as the land of endless opportunities. They arrived in staggering numbers. In 1820, the U.S. population was 9.5 million and its average annual increase was 240,000. By 1901, the corresponding totals were 77.6 million and 1.5 million.
The immigrants were capable, and they worked hard.

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