Scientists who conducted three studies published in the Science and Nature journals showed that horse domestication changed the genetic structure of Eurasia. The successive invasions led by the Huns and Mongols supplant western Indo-European farmers in an incremental westward drive that also brought Hepatitis B and plague. The Huns were a nomadic people who lived in Eastern Europe, the Caucasus, and Central Asia between the 4th and 6th century AD. The three studies reported sequencing the genomes of dozens of humans who lived between 2,500 BC and 1,500 AD, a 4,000-year period from the Iron Age to medieval times. Their analysis showed a slow and steady shift in the genetic makeup of the people who populated the Eurasian steppe, a massive expanse stretching from Hungary and Romania in the west to Mongolia and northeast China in the east. According to the data, the steppe population changed "from being of mainly western Eurasian genetic ancestry to east Asian genetic ancestry," said Eske Willerslev of the University of Copenhagen, who co-authored two of the studies. "Its also changing the steppe in terms of being Indo-European speakers to becoming Turkish-speaking people," he noted. The Indo-European language group gave rise to English, French, German, Russian, Hindi, and Persian languages, while Turkish is part of the Turkic language group including Mongolia. The Scythians, an Iranian population who occupied the steppes from about 800 to 200 BC, were replaced by the Huns coming from Mongolia. Willerslev said that the genetic makeup of contemporary people in this 8,000 kilometer-long stretch across Europe and Asia has mainly been formed within the last 1,000 years. Scientists explained that horse domestication and riding, and arrow making, led to the infusion of a military dynamic into the steppe, and to a constant changes in empire and the genetic makeup of conquered populations. The researchers also found that the Justinian plague pandemic, which killed millions of people on the European continent in the years 541 and 542, had come with the East Asian conquerors, while Hepatitis B, which kills almost a million every year due to complications such as liver cancer, was already present in Eurasia some 4,500 years ago.