Why are there so many poor gang infested areas in USA, is Europe like this?

There aren't. The US has a population of 300 million. The vast majority of the country is extremely safe. Gang activities are typically in major cities. A variety of social factors are typically the result of these... economic systems, education systems, health care issues, lack of sex education/teen pregnancies, immigration, gun control, drugs prevention, etc.

Europe now has many of the same issues. There are areas of France, Spain, Germany, etc. which now run 40% unemployment, 70% youth unemployment, which suffer riots, and which a 'no go' areas for police or certain ethnic communities. Areas of Sweden, Norway, Denmark, etc. have massive crime spikes in certain 'ethnic' enclaves and a flight of those of other races/religions.

Japan simply does not permit large scale immigration so there isn't really gangs on that level. Canada and Australia have high inner city crime, but its still a lot less than the US or Europe.

It was created that way on purpose. They call it "urban planning". If you plan to cram lots of people into a small area, then that's exactly what is going to happen. If you demoralize them in the process, through things like alcohol, drugs, strip bars, gambling, dumb jobs, mass immigration of very poor people, mass immigration of refugees, lots of trashy fast food like Mc Donald's, tattoo and piercing parlors; then on the level of proactive demoralizing culture creation: give them dumb *** standard education, tons of music, tons of sports, tons of movies, tons of amusement and entertainment. When you finally have created enough people who will do your every bidding for money, you create new crimes for your newly conditioned gang class. Perfect way to have the poor occupied with the poor - everyone is busy with the job of selling your drugs or putting the sellers in prison or just perpetuating your culture of corporate trash jobs.

USA has not dealt with the problem effectively, but I suspect a few European etc locations are almost as dangerous.