Why did the titanic sink even though it was deemed to be unsinkable?

RMS Titanic was a passenger liner that sank in the North Atlantic Ocean on 15 April 1912 after colliding with an iceberg during her maiden voyage from Southampton, UK to New York City, USA. The sinking of Titanic caused the deaths of 1514 people in one of the deadliest peacetime maritime disasters in history. She was the largest ship afloat at the time of her maiden voyage.

Figure of Titanic's hull

            How did the Titanic sink then? The Titanic was claimed to be nearly unsinkable and this gave passengers the false impression that it was a very safe ship. The Titanic struck an iceberg at around midnight on the 14 of April 1912. However, they have received warnings beforehand on there being pack ice around and even big icebergs. This is due to the fact that the ship’s “wireless” system was a bit faulty at the time when those warnings were issued and the radio operator just ignored most of the warnings.

            

What made the Titanic sink the way it did then? The Titanic was warned that there was an iceberg right ahead just 1 minute before collision and officers tried to ‘port’ the ship by swinging the bow around the obstacle and then swing the stern so that both ends of the ship will avoid a collision. However, this process was delayed by some error in relation of the message. Titanic barely avoided a head-on collision but the change in direction still caused the ship to strike the iceberg with a glancing blow. 

Figure of Titanic 'Porting around'

An underwater spur of ice scraped along the starboard side of the ship for about seven seconds; chunks of ice dislodged from the upper parts of the iceberg fell onto he forward decks. A few minutes later, all of Titanic’s engines stopped. The tear caused by the scrape caused about 7.1 tons of water to gush in every second. This filled up 5 of its 16 watertight compartments. However, the Titanic was only designed to have 2 of its compartments flooded and at most 3-4 compartments at different parts of the ship. This caused the titanic to tilt a bit and when pressure was mounting near the middle of the ship, this caused the middle of the ship to split into two and it just sank into the bottom of the ocean where the pressure is as high as 6500 pounds per square inch.