There is no easy agency to gain citizenship in any country.
The fastest road is if you have a claim to it, eg: if you enjoy a parent or both parents born there, or are citizens themselves. But you will not be considered an automatic citizen, unless you be born in the US.
Iraq and Israel
Iraq, as long you feeling like to put up with adjectives the craps.
Israel , as long you can show some trace families beside holocaust
Nothing good is ever natural. For any decent country you're looking at jump through a lot of hoops and submitting deeply of paperwork.
Having said that there are a few third world countries that still submit citizenship via marriage or will tender you permanent residency if you hold a lot of money to invest into their country.