Short answers, pulled from the story.
The Seleucid Empire was founded in 312 BC by Seleucus I Nicator, a Macedonian general who had served as Commander-in-Chief of the Companion cavalry under Alexander the Great. Seleucus established himself in Babylon that year after receiving Babylonia and Assyria following the division of Alexander's empire.
The Seleucid Empire ended in 63 BC when the Roman general Pompey abolished it after reorganizing the Hellenistic East. By then the empire had already been reduced to Antioch and a few Syrian cities, and Pompey removed both rival Seleucid claimants, Antiochus XIII and Philip II, making Syria a Roman province.
At its greatest extent the Seleucid Empire covered Anatolia, Persia, the Levant, Mesopotamia, and territories corresponding to modern-day Iraq, Iran, Afghanistan, Kuwait, and parts of Turkmenistan. The empire stretched from the Aegean Sea to what is now Afghanistan and Pakistan.
The Seleucid-Mauryan War ended in a treaty between Seleucus I and Chandragupta Maurya. Chandragupta received territory west of the Indus including the Hindu Kush and modern-day Afghanistan, while Seleucus received five hundred war elephants that played a decisive role at the Battle of Ipsus in 301 BC. Seleucus also sent an ambassador named Megasthenes to Chandragupta's court at Pataliputra.
Antiochus IV Epiphanes provoked the Maccabean Revolt through aggressive Hellenizing policies, including replacing the moderate high priest Jason with the radical Hellenist Menelaus via a bidding process, plundering the Jerusalem temple, and banning traditional Judean practices. He interrupted the daily sacrifice for three years and six months, leading to a full-scale armed rebellion the weakened empire could not suppress.
Rome defeated Antiochus III the Great at the battles of Thermopylae in 191 BC and Magnesia in 190 BC. The resulting Treaty of Apamea in 188 BC required the Seleucids to pay a large indemnity and permanently relinquish all territory west of the Taurus Mountains, with former Seleucid lands in Anatolia going to Rome's allies, the Kingdom of Pergamum and the Republic of Rhodes.