Qin's wars of unification
Most accounts start with Qin's attack on Han in 230 BCE; Chinese Wikipedia counts from Qin's attack on Zhao in 236 BCE.
Sides
Han, Zhao, and its successor state of Dai, Yan, Wei, Chu, and Qi
Countries today: 
China
What happened
Between 230 and 221 BCE the state of Qin, in the west of the Warring States, defeated the six other states one after another. King Ying Zheng of Qin sent his armies first against Han, the weakest, whose capital fell in 230 BCE. Zhao's capital Handan fell in 228 BCE, after the Zhao king had his general Li Mu, who had held Qin off, put to death. In 227 BCE Jing Ke, an assassin sent by the crown prince of Yan, failed to kill the Qin king; Qin armies took the Yan capital the next year. Qin flooded the Wei capital Daliang in 225 BCE, lost one army to Chu, then sent a far larger one under Wang Jian that took the Chu capital in 223 BCE. The last Yan forces in Liaodong were defeated in 222 BCE, and Qi surrendered without fighting in 221 BCE. Ying Zheng then took the title First Emperor. No reliable count of the war's dead survives.
Outcome: Qin ruled the lands of all seven states; Ying Zheng took the title Shi Huangdi, First Emperor, and divided the empire into 36 commanderies.
Key events
Leaders
- Ying Zheng (Qin Shi Huang) · King of Qin; First Emperor from 221 BCE · The state of Qin
- Wang Jian · Qin general against Zhao, Yan and Chu · The state of Qin
- Wang Ben · Qin general against Wei, Yan and Dai · The state of Qin
- Li Xin · Qin general; led the first, failed campaign against Chu · The state of Qin
- Meng Wu · Qin general in the campaign against Chu · The state of Qin
- Li Mu · Zhao general who held Qin off; put to death by his own king · The six other Warring States, each fighting Qin on its own
- Crown Prince Dan of Yan · Sent Jing Ke to kill the Qin king · The six other Warring States, each fighting Qin on its own
- King Xi of Yan · Last king of Yan, captured in 222 BCE · The six other Warring States, each fighting Qin on its own
- Xiang Yan · Chu general; defeated Li Xin, then lost to Wang Jian · The six other Warring States, each fighting Qin on its own
Cultures it ended or changed
Meanwhile, elsewhere in
- Maya civilization
Mesoamerica · Longest-lasting hereThe Maya Long Count calendar tracks days in an unbroken count from a mythical starting point in 3114 BCE.
- Ancient RomeRoma
Europe · - Ancient EgyptKemet (km.t)
Africa · Oldest here (disputed dates)The Ptolemies' Alexandria, with its lighthouse and library, grew into a city of hundreds of thousands while Qin's First Emperor unified China in 221 BCE and Rome fought Carthage.
- Paracas culture
South America · The richest Paracas mummy bundles wrapped a single body in layer upon layer of cloth, sometimes more than a hundred separate textiles.
- Zapotec civilizationBe'ena'a Mesoamerica ·
Zapotec nobles were buried in stone tombs beneath their own houses, later reopened and reused for centuries.
- Celtic Iron Age
Europe · Celtic peoples left almost no writing of their own; nearly everything known about their beliefs comes from Greek and Roman authors who saw them as enemies.