Kung Fu is more of an open hand style. Karate is closed fist. I saw a tournament of different fighters and the Kung Fu style was graceful, but when it came to striking, they had to use closed fists like everyone else.

Karate is Japanese and Kung Fu is chinese.

Firstly Karate is Japanese and Kung Fu is Chinese. After that there are just too many differences to name.
Whichever you decide to study, try to remember neither is about fighting. Both are a way of life, a philosophy, and as such can be applied to every aspect of a persons existance.
Don't just take the class, study as well. Go to the library and read books. There is so much more to both than you could ever imagine. For a start just Google 'The philosophy of karate / kung fu' and see what comes up. just that one action could set you on a wonderous journey of education and excitement.

One is Japanese and the other is Chinese. Is the most obvious. I believe back in the 40s 50s after WW II, Karate was introduced to the USA by mostly American military personnel that fought in the Pacific campaign. While it seems the Chinese have long been in the U.S. they were much more secretive about sharing their martial arts. This was going on well into the 60s and early 70s. Also Kung Fu seems more available on the west coast in places like California. They're also far too many different styles of Kung Fu and Karate to say exactly what the differences are. Some are more hard line linear and some are more circular. Then are some that are a little of both. So unless you are asking about one specific style then its very hard to say exactly.

Karate=
Hard
Okinawan
External
Power oriented

Kung Fu=
Soft
Chinese
Internal for the most part.
Speed oriented.

Karate and Kung Fu aren't a style, they are a system of styles.

Karate has many styles along with Kung Fu.

Karate:
Shotokan Karate
Kempo Karate
Ishin Ryu Karate
and much more.

Kung Fu:
Wing Chun (What I take)
Praying Mantis
Tai Chi
And hundreds more.

Why is there more Karate than Kung Fu in America? After WW2 when the Americans defeated the Japanese, they had a check point in Okinawa and the Marines forced the Okinawans to teach them the art, then when they brought it back to America, they spread it and added the belt system to it. At the time, the Chinese prohibited teaching Kung Fu to westerners until Bruce Lee broke the gap between East and West which was in the 1960's. That's why Karate is more known than Kung Fu. Atleast that's what I read.

Hope this helped.

Kung fu is a generic label for Chinese martial arts, doesn't actually have anything to do with martial arts. There are many different styles and they are vary as to what types of techniques they teach.
Karate is also more or less a generic label for martial arts from Japan/ Okinawa, means open hand. Again many different styles with different focuses on what they teach.
As to why there are more Karate schools than Kung fu schools, several reasons. One of the main ones being the "Kung fu craze" of the 70's, it kind of resulted in lots of bubble gum schools or as a lot of people on here call them McDojo's. These are basically money makers for the people who run them, they basically feed you a lot of BS and don't really teach too much worth anything. In my opinion Chinese martial arts and Tae Kwon Do have been there worst effected by this.
There are plenty of really good Kung fu, Karate and TKD schools out there, you just have to check them out pretty good before you go signing contracts and giving your money away.
Be mindful and check a school out before joining.
Best of luck

Karate is Japanese hand-to-hand, while Kung Fu is a Chinese term for Great Achievement in any field technically. Wu Shu means Martial Arts in Chinese. Karate is copied from a few Chinese styles. There is a wider range of moves in Chinese styles. Chinese boxing styles have dichotomies. They are divided into Buddhist = Shaolin and Taoist = Tai Chi Chuan and into Northeren and Southern styles. Japanese are not as racist as Chinese are. Many Chinese do not teach their martial arts to non-Chinese.