Figure 1: This table is a breakdown of all foreign-born players in the MLB. Note that within the Latino countries, the Dominican Republic has the largest representation in the MLB. Also, when put together, the Latino countries make up 85% of the foreign-born players represented in this study.

Figure 2: This chart looks at the presence of foreign-born players throughout history. As you can see, this presence increases throughout the century, especially during the last 20 years.

These tables are from "Coming to America: Immigrants, Baeball, and the Contributions of Foreign-Born Players to America's Pastime" by Stuart Anderson and L. Brian Andrew.