Complex sentence: By that time it had become difficult for Mexican medical graduates, to receive further training and specialization in the United States, which still has the lead in many aspects, such as health care development and application of technology in medicine.
Split into simpler sentences: By that time it had become difficult for Mexican medical graduates, to receive further training and specialization in the United States. Which still has the lead in many aspects, such as health care development and application of technology in medicine.