Why we say La/Le in front of a noun/name

AW Michot Definite Articles
The definite articles, le, la, les, are basically equivalent 
to English the. Anytime the is used in English, a definite 
article will surely be used in French. In some cases, however, French will 
use a definite articles when English uses no article at all.
This includes times when a group of nouns is referred to in 
its entirety. For example when blanket statements are made about all cockroaches, 
all humans, or all cars.
Les blattes vivent dans les murs et se reproduisent 
Cockroaches live in the walls and reproduce prodigiously. 
Les baleines sont les animaux les plus grands du monde. Les 
humains, en comparaison, sont très petits.
Whales are the largest animals in the world. Humans, by comparison, 
are very small.

Il pense que les voitures sont l'invention du diable.
He thinks that cars are the invention of the devil. 
...and when a noun is referred to in a general sense (for 
example a statement that refers not to a particular war but to war in general).
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