The Nippon Baseball League is a little upset about Boston's decision to sign Tazawa: they feel that a gentleman's agreement regarding the cherrypicking of talent has been violated by the pursuing and capturing of one of Japan's more high-profile amateurs.
I'll admit to some bias here, but that reaction seems like sour grapes. Like other professional sports, baseball has really become a global concern, bringing with it the sink-or-swim mentality of marketplace economics to the sale of product to consumers. When it comes to producing that product - to the hiring, training, and molding of groups of athletes into competitive baseball teams - the group with the most capable production staff is going to find the best materials. The realities of this situation aren't predisposed to American domination, either: from my understanding, the NBA is starting to find itself on the losing end of this global equation in basketball: the salary cap, which (supposedly) creates a more equitable playing field within the league, is now preventing NBA teams from competiting effectively with other leagues when it comes to signing talent. In other words, the NBA has a competitive disadvantage they may need to address.
The solution for the NLB, as for the NBA, is the same: offer an environment that makes your league more attractive (through whatever methods you think would be best to entice players) to the talent pool. Crying about broken agreements just makes you look lost and out of touch.