Constantine I was born circa 280 in Naissus, Moesia (now Niš, Serbia). His father became the Western Roman emperor in 305; after his father's death, Constantine fought to take power. He became the Western emperor in 312 and the sole Roman emperor in 324. Constantine was also the first emperor to adhere to Christianity. He issued an edict that protected Christians in the empire and converted to Christianity on his deathbed in 337.
The correct answer is D.
Many of the European countries involved in the era of imperialism had a large standing army. Countries like Great Britain and France had been around for centuries and built a strong military. The other three are all important factors that lead to the increase of imperialism in the 1800's.
