Used by eris in Greek Mythology to wreak havoc on folks. The golden apple of discord had been stolen from a tree belonging to Hera (Zeus's wife and goddess of wedding).(This ended up being connected by someone and I also believed I would offer and explanation).
(traditional mythology) a golden apple tossed into a banquet of the gods by Eris (goddess of discord--who wasn't welcomed); the apple had `when it comes to fairest' written on it and Hera and Athena and Aphrodite all advertised it; when Paris (prince of Troy) awarded it to Aphrodite it began a chain of activities that generated the Trojan War
"apple of discord" is used to represent the core, kernel, or crux of an argument, or a tiny matter that may result in a bigger dispute.
The arsenals of Pola and Cattaro were already in the hands of the insurgents; and the Emperor Charles, in the hope either of winning the favour of the new regime in Zagreb or of throwing an apple of discord between it and the Entente, signed a decree on Oct.