Did many of the Jedi fall to the dark side during the clone wars? As most of the Jedi didn't go on a lot of missions before the war. Then being thrusted into nonstop conflict, leading clones armies, befriending them and then watching them die.
I realized that my comment included Jedi that fell to the Dark Side possibly before the Clone Wars. Here are a few that fell to the Dark Side during the Clone Wars:
Billaba's final mission took her to the war ravaged world of Haruun Kal where she was to aid in an uprising against the Confederacy of Independent Systems. While conducting the mission, Billaba fell to the dark side, going mad in the process. When her former master sought her out, she attacked him after a prolonged hunt, resulting in her falling into a comatose state.
Around 20 BBY, after growing disillusioned with the Jedi Order during the Clone Wars, she orchestrated the bombing of the Jedi Temple, for which she framed Ahsoka Tano, resulting in Tano leaving the Order after her innocence was proved and Offee was exposed as the real bomber.
Bulq was therefore recruited by his colleague, Mace Windu, to assist in the refinement of Vaapad, Windu's new combat form. Vaapad required that the user dance along the edge of the dark side of the Force, however, and Bulq fell captive to the darkness. He pursued his studies of the dark side in secret until Count Dooku captured him during the earliest days of the Clone Wars and turned him fully to the dark side.
Vos had an ongoing struggle with the dark side of the Force, particularly after he sustained recurrent amnesia after he overdosed on an illegal drug administered by an enemy shortly after the Battle of Naboo. The Sith Lords Darth Sidious and Darth Tyranus both showed an interest in him, and while Vos served Dooku for a while, he eventually redeemed himself and was readmitted into the Jedi Order.
During the war, Krell foresaw how the Republic would be destroyed from within, thus paving the way for the rise of a New Order. This vision, coupled with his lust for power, ultimately caused Krell to abandon the Jedi way. Outwardly, he maintained the appearance of his ties to the Jedi and Republic. In secret, Pong Krell had embraced the dark side of the Force.
Anakin becomes Darth Vader.
I'm not including Ahsoka Tano's temporary fall on Mortis because that wasn't really related to the Clone Wars.
In the EU there is one very well documented case of Jedi falling to the Dark Side during the Clone Wars. The Bpfasshi Dark Jedi crisis, first mentioned in Timothy Zahn's Heir to the Empire novel, was a case where several Jedi on Bpfassh fell to the Dark Side. They caused havoc across the Sluissi sector, including kidnapping smuggler chieftain Jorj Car'Das, until the final Dark Jedi was stopped; by Yoda, at Dagobah.
"The Bpfasshi don't like Jedi. They had some trouble with Dark Jedi during the Clone Wars, and chased them as far as Dagobah." ―Leia Organa Solo, to Luke Skywalker
EDIT: jliv902's comment reminded me of the obvious case of Anakin Skywalker falling to the Dark Side. Voss also fell, maybe, since he was allegedly a double-agent. Others, such as C'Baoth and Dooku, fell before the War.
In Legends, there were numerous Jedi who fell to the Dark Side during the Clone Wars. However, in the current Disney canon, there are a lot fewer. Two Jedi are confirmed to have fallen during the Clone Wars (beside Anakin Skywalker):
Vos fell to the Dark Side after being instructed in the Dark Side by Asajj Ventress, then tortured by Count Dooku. His fall was confirmed by Yoda:
Gently, Yoda reached and placed a small hand on Kenobi’s. “Vos, saw I today. Acknowledged his aid through his unique skill, I did. Touched I his hand, through which flows the Force. Able at times, I am, to see that which is hidden. The Force was with me this day. The truth to me has been granted. Taken by the dark side, Quinlan Vos has been, though conceal it well, he does.” Yoda hesitated. “Lost to us, I fear he is.”
Krell sought to become Count Dooku’s apprentice, so I think we can say he was pretty fallen. From "Carnage of Krell":
KRELL: Not yet. But when I get out of here, I will be. After I’ve succeeded in driving the Republic from Umbara, the count will reward my actions and make me his new apprentice.
Another Jedi who may or may not have fallen to the Dark Side is Barriss Offee.
That no other Jedi fell to the Dark Side seems fairly likely. Vos’s betrayal was seen as nearly unprecedented, and only Krell and Offee’s names was mentioned when discussing it:
“This is by far the greatest breach of trust the Jedi have seen since Count Dooku himself betrayed us,” Mace said. “Even General Krell’s deception did less damage. Vos isn’t just a Jedi, he’s a Jedi Master with unique skills. And he is a Jedi Master in wartime who has worked side by side with Dooku. This is going to have massive repercussions.”
Actually the exact truth is uknown but many believe that quite a few fell to the darkside believing that either they would be killed if they stayed light or that the jedi were too weak and the sith should rule.but many also stayed in the light side lead by halagad ventor who with the help of qu rahn created a jedi network helping the remaining jedi to make a small rebeliance wich was crushed when Vader apprehended halagad and tortured him until he revealed the base and the network