http://www.absoluteanime.com/zoids/
Zoids Chaotic Century/34 eps/Pioneer
Once long ago, on Planet Zi, an ancient civilization created biomechanical mechs called Zoids. The race has disappeared, but Zoids still remain.

The story of Zoids Chaotic Century is split into two parts. The first part take place during a titanic war between the two greatest nations on Zi: the Guylos Empire and the Helic Republic. Into this chaos enters three different yet connected lives: Van Flyheight, a young Republican who stumbles upon some ancient ruins; Zeke, an Organoid in the ruins who has the capacity to revive and mazimize the potential of Zoids; and Fiona, an ancient Zoidian awakened from her sleep and who now accompanies Van on his journey into destiny. With the help of the kooky Dr. D, the mercenary Irvine, and the independent Moonbay among others, Van inadvertently finds himself on a course to stop the war before it takes a disastrous turn.

The second part takes place four years after the peaceful resolution of the war. In an effort to help prevent future wars, a Guardian Force is jointly established by the Empire and the Republic. Its mission is to seek out volatile groups and contain them before they can cause more chaos. Van and Zeke are among the Guardian Force\\\'s key members, and those they met in their previous adventure come back in this new chapter. It is duirng this period that more of the Zoidian secret is revealed as the true battle for the of planet Zi begins.



Zoids Guardian Force/33 eps/Cartoon Network
Zoids Guardian Force takes place after Zoids Chaotic Century. Four years have passed, making Van 18 years old now. He is the newest member in a group established by the Empire and Republic, the Guardian Force. Van is now with Fiona. They both have feelings for each other, and seem like a nice couple. Together with Zeke, the trio set out to fulfill the duties of the Guardian Force- to protect the citizens.

They all meet Thomas Shubaltz, the younger brother of Karl Shubaltz. Thomas has this big crush on Fiona, but doesn\\\'t dare say it. He totally hates Van, just like Raven. Rhyss (or Ryss, or Rhys, or Reese) and Hiltz seem to pester Raven a lot in this series too.



Zoids New Century Zero/26 eps/Pioneer
The teams are deployed, and the battlefield is set. Ready...FIGHT!

The Chaotic Century of planet Zi has long since passed into the pages of history. The Zoids that were once instruments of war and destruction now find a place in a new order and a new sport: organized Zoid combat. Originally an unofficial sport, the realm of ruthless groups looking for power and control, that all changed with the establishment of the Zoid Battle Commission, which codified the rules of combat, established official leagues and events, and provided a means of enforcing the rules. Zoid battle thus emerged into the mainstream.

Teams of Zoid pilots battle each other to become the top dog in the leagues, and the Blitz Team is preparing to rise to the challenge with the help of a pair of newcomers: Bit Cloud and the unpredictable Zoid Liger Zero.

In this new world of organized mech combat, there still dwell elements of chaos, none more dangerous as the Backdraft Group, a rogue Zoids organization out for personal gains and power. Between this and the remaining teams in the league, Blitz Team has its work cut out, but if Bit Cloud is any indication, they\\\'re not afraid.

Though the anime is very new, the concept of these mechanical machines actually dates back to the 1980s, with a set of innovative mechanical model kits. The kits were re-introduced in Japan in 1999, with the anime as support. Though the first series to appear in the US, it is really the sequel to Zoids Chaotic Century.




ZOIDS FUZORS/26 eps
In Blue City, Zoid battles are held within a stadium, and, as with the Zoid battles of Zoids New Century Zero, there is money to be won by the strongest team. However, some Zoids are now able to merge as one, forming a superior machine. Enter RD is a young, skilled Zi fighter who has aspirations of being the best Zoid pilot on Planet Zi!

Zoids Fuzors is basically the fourth season if you consider Chaotic Century (1st), Guardian Force (2nd), and Zoids New Century Zero (3rd).