Recent tensions with Iran have sparked renewed interest in the US military draft.The US doesn't have a draft and is unlikely to reinstitute one, but if it did, there are number of reasons many Americans wouldn't get selected.Visit Business Insider's homepage for more stories.We're barely into a new decade, and already many are worried about another world war.Whether the targeted killing of an Iranian general could spark a global conflict is irrelevantat least it seems to be for anyone watching Twitter and Facebook. Millennials and Gen-Zers rushing to find out whether they could be drafted actually crashed the Selective Service information website.To be clear, the United States doesn't conscript its citizens and hasn't done so since 1973. President Jimmy Carter created the Selective Service System in response to the Soviet invasion of Afghanistan in 1979 as a means of keeping tabs on military-age males.You know, just in case.Since the draft ended, however, US demographics have shifted. Carter likely never considered the idea of transgender women signing up for the draft, for example. Americans themselves have changed as well, and not always for the better.In fact, the majority of Americans couldn't be drafted if they wanted to be. Here are the six top reasons why:SEE ALSO:Here's all the extra pay that US troops could get for being sent to the Middle East on short notice1. ObesityHere's the biggest reason Americans can't join the military. Literally. The same lawmakers who deemed ketchup a vegetable in schools are now surprised there's an obesity epic among children.In 2015, then-Maj. Gen. Allen Batschelet, head of Army Recruiting Command, predicted that, by 2020, half of all military-age men and women would be too obese for military service. The numbers were trending that way, anyway.Welcome to 2020, where some 15,000 people who try to join the armed forces every year are turned away due to weight-related issues. The problem is so bad military leaders believe it's a threat to national security.2. EducationThe United States military wants its troops to have at least a high-school education or the equivalent. It isn't just about a basic understanding of core concepts. It also indicates a potential service member's ability to complete organized programs, including study and fitness regimens. Some sources believe the rates of graduation are over 83% and trending higher, but other metrics show a trend in the opposite direction.While the military breaks down its recruiting pools into categories, the vast majority of accepted candidates are Category I recruits. While some services will accept applicants with a GED, they don't score as high on the Armed Forces Qualification Test and tend to fall into lower categories, according to a 2005 Rand Corporation study.That same study found that candidates with a GED can be up to 30% less effective at their jobs, so some branches won't even consider them. The Pentagon goes so far as to limit how many candidates from Category IV, the lowest category based on education and AFQT scores, the services can recruit.If there is a draft in the coming days, those recruits certainly won't make it into the Air Force or Coast Guard, the branches of service with the highest minimum ASVAB and education standards.3. Criminal recordsOne out of every 10 American adults cannot join the military because they have a criminal history, says Mission: Readiness, a nonprofit organization comprised of retired generals and admirals.This keeps some 3.4 million adults out of the military, even if they meet all the other standards of service. More than one million juveniles are arrested every year, and more than half of those become repeat offenders in their lifetimes, including felony-level convictions.In fact, a Pew Center for the States study revealed in 2008 that one of every 30 men of ages 20-34 is behind bars. It'd be hard to meet the draft board if the warden won't let you leave jail.4. Health problemsMission:Readiness also found an estimated 32% of America's greatest natural resource have some kind of health problem that would disqualify them from serving in World War III.These are the health issues unrelated to obesity, of course. Adding obesity to the health issues list put this number up to more than half of American children.Asthma, mental health issues and ADHD top the list of maladies that keep the recruiters at bay, says Mission: Readiness. Even those who currently serve can have health-related issues that keep them fromdeploying, such as dental problems and recurring injuries.5. DrugsThe days of getting high and earning the Medal of Honor are long gone, unless you're playing the "Medal of Honor" video game series.The number of American youth who admit to using recreational drugs on a regular basis is enough cause for concern when it comes to military recruiting. But when paired with drug and alcohol abuse, there come convictions for driving under the influence and other drug- and alcohol-related charges. All of these will render people unfit to serve.6. The usual reasonsThere's only one Steve Rogers, and he's a fictional character. Even among the fit, drug-free, educated masses, many will still be too short, too tall, have flat feet or be the single parent of a minor child.All of those reasons will keep someone out of the military in general, but each branch has its own particular limitations.Too many tattoos' Forget about the Marine Corps. Can't score high enough on the ASVAB' The Air Force isn't for you.And all this is long before they ever look you up on social media. Click here to read full news..