Abbrev.
Religion
Between 10 & 20
200

A regional alliance:
NATO

North Atlantic Treaty Organization

200

In Judaism this day of atonement is the holiest of all days 

Yom Kippur

200

It's the smallest 2-digit prime number

11

400

On the clock in Denver:
MST

Mountain Standard Time

400

During this holy month of fasting, many Muslims will recite the entire Koran, a portion each day

Ramadan

400

This number becomes palindromic when written with 3 letters in Roman numerals

XIX

600

Let the games begin:
IOC

International Olympic Committee

600

In the King James version of the Lord's Prayer, they're the 4 words that follow "Our father which art in heaven"

hallowed be thy name

600

When writing a haiku, you must use this many syllables

17

800

The address of a web page:
URL

uniform resource locator

800

This religion at the end of the alphabet was founded by a Persian prophet & pre-dates Islam

Zoroastrianism

800

DAILY DOUBLE

Georgia ratified this amendment into law December 6, 1865

1000

A care provider:
LPN

licensed practical nurse

1000

The Hindu goddess Durga, also known by this shorter "D" name, fights for Dharma & rides a lion

Devi

1000

Developed by chemist Willard Libby, this method named for an isotope is used to date fossils

Carbon-14 dating