The 1453 conquest of constantinople is an important turning point in global history because it

1.

ushered in pax romana
2.

began the middle ages
3.

contributed to the rise of the ottoman empire
4.

signified the end of the napoleonic wars

Well it isn't 1 because Pax Romana happened way before 1453, Middle ages began in 400CE and lasted until 1400CE. The Napoleonic Wars happened about 350 years later. So through just the process of elimination you can know its 
4. Contributed to the rise of the Ottoman Empire.
The ottoman did a series of attacks against Constantinople but the still they were kept out of the walls, eventually the to be Turks did finally capture the city in 1453  

The answer is option b and c.

Iraq because its lack of policing and government concern