In biology, kingdom (Latin: regnum, plural regna) is the second highest taxonomic rank, just below domain. Kingdoms are divided into smaller groups called phyla. Traditionally, some textbooks from the United States used a system of six kingdoms (Animalia, Plantae, Fungi, Protista, Archaea/Archaeabacteria, and Bacteria/Eubacteria) while textbooks in Great Britain, India, Australia, Latin America and other countries used five kingdoms (Animalia, Plantae, Fungi, Protista and Monera). Some recent classifications based on modern cladistics have explicitly abandoned the term "kingdom", noting that the traditional kingdoms are not monophyletic, i.e., do not consist of all the descendants of a common ancestor. 

When Carolus Linnaeus introduced the rank-based system of nomenclature into biology in 1735, the highest rank was given the name "kingdom" and was followed by four other main or principal ranks: class, order, genus and species. Later two further main ranks were introduced, making the sequence kingdom, phylum or division, class, order, family, genus and species. In the 1960s a rank was introduced above kingdom, namely domain (or empire), so that kingdom is no longer the highest rank. 

Prefixes can be added so "subkingdom" ("subregnum") and "infrakingdom" (also known as "infraregnum") are the two ranks immediately below kingdom. Superkingdom may be considered as an equivalent of domain or empire or as an independent rank between kingdom and domain or subdomain. In some classification systems the additional rank "branch" (Latin: "ramus") can be inserted between subkingdom and infrakingdom (e.g. Protostomia and Deuterostomia in the classification of Cavalier-Smith).
Which rank is this article about?
What is above it?
And below it?
How many kingdoms does the US recognize?
And elsewhere?
How many kingdoms do they agree on?
Which ones are those?
What kingdoms does the US have that the others don't?
And which ones do others have that the US doesn't?
Who created this system?
When?
What science is this part of?
Was kingdom the highest rank at first?
Is it still?
Why not?
What's another name for domain?
Originally how many ranks were below kingdom?
What were they?
Is it still like that?
What happened?
Kingdom
In biology, kingdom (Latin: regnum, plural regna) is the second highest taxonomic rank, just below domain.
domain
In biology, kingdom (Latin: regnum, plural regna) is the second highest taxonomic rank, just below domain
phyla
Kingdoms are divided into smaller groups called phyla.
Six
 Traditionally, some textbooks from the United States used a system of six kingdoms 
Five
raditionally, some textbooks from the United States used a system of six kingdoms (Animalia, Plantae, Fungi, Protista, Archaea/Archaeabacteria, and Bacteria/Eubacteria) while textbooks in Great Britain, India, Australia, Latin America and other countries used five kingdoms (Animalia, Plantae, Fungi, Protista and Monera).
Four
 (Animalia, Plantae, Fungi, Protista, Archaea/Archaeabacteria, and Bacteria/Eubacteria) while textbooks in Great Britain, India, Australia, Latin America and other countries used five kingdoms (Animalia, Plantae, Fungi, Protista and Monera).
Animalia, Plantae, Fungi and Protista
Animalia, Plantae, Fungi, Protista, 
Archaea/Archaeabacteria, and Bacteria/Eubacteria
Traditionally, some textbooks from the United States used a system of six kingdoms (Animalia, Plantae, Fungi, Protista, Archaea/Archaeabacteria, and Bacteria/Eubacteria
Monera
and other countries used five kingdoms (Animalia, Plantae, Fungi, Protista and Monera
Carolus Linnaeus
When Carolus Linnaeus introduced the rank-based system of nomenclature into biology in 1735,
1735

When Carolus Linnaeus introduced the rank-based system of nomenclature into biology in 1735
biology
In biology, kingdom (Latin: regnum, plural regna) is the second highest taxonomic rank,
yes
When Carolus Linnaeus introduced the rank-based system of nomenclature into biology in 1735, the highest rank was given the name "kingdom" 
no
In biology, kingdom (Latin: regnum, plural regna) is the second highest taxonomic rank, just below domain. 
in the 1960s a rank was introduced above kingdom
In the 1960s a rank was introduced above kingdom, namely domain (or empire), so that kingdom is no longer the highest rank. 
empire
Superkingdom may be considered as an equivalent of domain or empire
four
 in 1735, the highest rank was given the name "kingdom" and was followed by four other main or principal ranks:
class, order, genus and species
 in 1735, the highest rank was given the name "kingdom" and was followed by four other main or principal ranks: class, order, genus and species
no
Later two further main ranks were introduced, making the sequence kingdom, phylum or division, class, order, family, genus and species. 
later, 2 other ranks were introduced
Later two further main ranks were introduced, making the sequence kingdom, phylum or division, class, order, family, genus and species.