The key for a successful national team is to have a successful competitive domestic league. The trouble with the MLS is that it is competitive but not at a high enough standard. This is why a lot of players either come late in their career to the MLS or move abroad to play in Germany, England etc.
For the league to produce a lot of young talent and then improve them up to a high standard, the league needs to invest more or allow clubs to invest more to attract the better worldwide players to come into the MLS and improve the overall quality. Hopefully this will then have a knock-on effect and further down the line help the international team compete with the best nations in the world.
A lot of people say that it will always be tough with the other major US sports taking the best players but the US is a huge nation, the facilities are incredible for youngsters (compared with the UK) and the US knows how to market sport leagues to a high standard. I just think they need to invest to get more back.