Why have many of the khmer rouge leaders responsible for killing millions of cambodians never been brought to justice?

Why was it difficult fpr unions to succeed in the 1800s

What was the final spark that ignited the “european powder keg” and started world war 1

What important discovery was made by edmond halley and alexis clairaut, using newton's ideas of mathematics and gravity? they created the scientific method to outline how science should be conducted. they were able to find the orbit of a comet and predict the year of its return. they discovered the three newest planets--uranus, neptune, and pluto. they explained why objects appear to have color.