It stemmed from the annexation of the Republic of Texas by the U.S. in 1845 and from a dispute over whether Texas ended at the Nueces River (the Mexican claim) or the Rio Grande (the U.S. claim).
The correct answer is option D. "Companies replaced hand-operated brakes with air brakes on trains". The development of air brakes on trains was a significant improvement of railroad safety. Air brakes function much more faster than hand-operated brakes, because hand-operated brakes required that the brakemen turned the brakes in one car and jump to the next to set the brakes on, and so on.
Led China to become involved in the war
If you are meaning the Black Death (Bubonic Plague) the answer is:
It spread from Italy to Russia. It affected majorly in The cities Paris, Vienna, Venice and Genoa. It took 4 years.
