One of the interesting stories of the African Cup of Nations is that of Salomon Kalou. His path to international football stardom has been one of the most confusing and closely watched of his generation. He was born in 1985 in the Ivory Coast, but like many young African talents, he emigrated at a young age to play in Europe. In his case, he went to the Netherlands to play for Feyenoord in Rotterdam. He quickly became one of the best young forwards in Europe, and his star began to rise. In the months before the 2006 World Cup, his native Ivory Coast qualified for the tournament and called him up to play for the national team. Kalou surprised many by refusing, and instead decided to pursue Dutch citizenship so he could play for the Netherlands.

Why would a young Ivoirian do such a thing? It could be argued that the Netherlands is the more prestigious team. The Dutch won a European Championship and twice finished runner-up in the World Cup. But there’s also the Kalou family’s personal history: after a terrible showing at the 2000 African Nations Cup, the ruling military government sent the Ivoirian national team to a military base for three days of hard labor, broadcast live on national television. Kalou’s brother, Bonaventure, was on that team. Perhaps it’s not an enormous surprise that Bonaventure would counsel his brother to represent a different nation.

Salomon’s is just one of many intriguing stories surrounding the migration of football labor. Indeed, nationality and international football have had a long and confusing relationship. In the middle of the 20th century, a footballer could play for as many nations as he wanted. Alfredo Di Stéfano, one of the greatest strikers to ever play the game, suited up for Argentina, Colombia, and Spain, and all in a span of just 10 years.

FIFA has since changed the rules so that an individual can play for only one nation. But it’s still complicated terrain. The two most common areas of confusion involve Franco-African players born in France and soccer-poor nations nationalizing foreigners.

In the case of Franco-African players, many are born in France to first-generation African immigrants. That usually means they’re eligible to play for France or their country of ethnicity. It’s not uncommon for a young Franco-African star to get called up simultaneously by France and the African nation of their parent’s birth. Some, like Arsenal fullback Bacary Sagna, choose to play for France. Sagna was born south of Paris to Senegalese parents. On the other hand, Andre Ayew, a young winger who is destined for big things, has elected to play for Ghana, despite his birth near Lille.

Those are pretty simple cases. Sometimes, it gets complicated. Freddie Kanoute was born in France and played for the French Under-21 national team. But as he got older, he found himself frozen out of the senior national team, and he requested to switch to Mali. FIFA agreed, and made a rule change so individuals could apply to switch national sides if they played for one nation’s youth team but hadn’t yet played for the senior team. Other players to make such a switch include former Arsenal striker Quincy Owusu-Abeyie. Owusu-Abeyie played for the Dutch Under-21 national team before switching to Ghana.

The other common form of peculiar football citizenship occurs when small, football poor nations import footballers completely irrespective of standard naturalization rules. In 2004, FIFA had to stop Qatar from fielding three Brazilians who were poised to take up Qatari citizenship for no other reason than they we’re really good at football. Among the trio was Ailton, the stocky Brazilian striker who dominated the German Bundesliga for Werder Bremen and Schalke from 1998-2005.

Ailton was the kind of player who was completely unfashionable and totally at odds with the Brazilian national team’s ultra slick image. Despite his talent and stats, he would have never gotten a shot with Brazil. So it’s understandable that he may have jumped at the chance to play for another nation, any nation. But that said, his only connection to Qatar was that the Qatari football federation wanted to not be as bad at football, and Ailton wanted to play in international competitions. What made it really bad was how thinly veiled the whole ordeal was. Qatar was offering Ailton a large payoff, but on top of that, it isn’t the type of country that just gives away citizenship. Like all the gulf states, citizenship is a closely guarded prize. In a ludicrously wealthy oil state like Qatar, where only 25% of the population has citizenship, naturalization means a lifetime of lucrative social services.

This type of situation takes common labor migration — mediocre Brazillians play in Japan, aging superstars get big paydays in Qatar or the United States, raw developing Nigerian wingers go to Ukraine — and confuses citizenship.

Of course, there are legitimate instances when a player from a traditional football powerhouse ends up, through legitimate migration, in a football poor nation. Take the completely ludicrous story of Toto Tamuz, who moved from Nigeria to Israel when he was 2 years old. His parents emigrated to Israel to work, but they ran into financial trouble and returned to Nigeria. They left a young Toto with Israeli friends, and he grew up ‘Israeli.’ Today, he plays for the Israeli national team. The story gets really nuts when you get into his lack of Judaism and the orthodoxy of the Israeli Interior Office, but the point remains: Tamuz is more Israeli than Nigerian, and it probably makes sense that he plays for Israel.

In the 21st century, our ideas of citizenship will be challenged by free trade and labor migration. The world of international football illustrates some of these issues. Of course, footballers have the advantage of celebrity and wealth. It’s quite different to be a Turkish cab driver in Germany, or a Mexican crop picker in Southern California. But it’s an enormous concept. What do we make of globalization of the world’s labor market? That question is often asked in the context of protecting domestic jobs, but it’s a question that’s particularly interesting in the context of America’s immigration reform debate. Do we really want to create an underclass of “guest workers” who can live and work here but never become citizens? But when does someone who is here to work and make remittance become “American?” What makes an “American?”

I imagine any major football team has a pretty good immigration lawyer on retainer.