Passage: The Japanese were interested in Portuguese hand-held guns. The first two Europeans to reach Japan in the year 1543 were the Portuguese traders António da Mota and Francisco Zeimoto (Fernão Mendes Pinto claimed to have arrived on this ship as well, but this is in direct conflict with other data he presents), arriving on a Chinese ship at the southern island of Tanegashima where they introduced hand-held guns for trade. The Japanese were already familiar with gunpowder weaponry (invented by, and transmitted from China), and had been using basic Chinese originated guns and cannon tubes called "Teppō" (鉄砲 "Iron cannon") for around 270 years before the arrival of the Portuguese. In comparison, the Portuguese guns were light, had a matchlock firing mechanism, and were easy to aim. Because the Portuguese-made firearms were introduced into Tanegashima, the arquebus was ultimately called Tanegashima in Japan. At that time, Japan was in the middle of a civil war called the Sengoku period (Warring States period).

Question: What does the term Sengoku refer to?
Warring States period