The Thirty Years War could have been called a world war

The Thirty Years War was fought with such savagery, death, and wanton destruction that if atomic weapons existed in that conflict, Caucasian people would exist only in history books today.

The term, "world war", is a 20th century invention. But there have been a number of historical military conflicts of wide enough geographical location and conflagration that, easily, would qualify for the term, world war. If those wars were awarded the term, world war, then World War II would be more like World War VIII.

Here's my list:

The Persian-Greek wars
The Ostrogothic, Visigothic, and Gothic invasions of the Roman empire
The Hunnic successive invasions of eastern then western Europe
The Mongol invasions of China, Central Asia, Russia, Japan, Southeast Asia
The Imjin War of 1592-97 (Japan's war with Korea and China)
The Thirty Years War
The Napoleonic Wars