This is a fairly controversial statement with as many people disagreeing as agreeing but global health is a bit of non-concentration.
In our increasingly internationalized society the distinction between local and global has been blurred: we witness a world that is constantly at war, natural disasters occur more frequently than at any time in history, displaced individuals, refugees and asylum seekers have become a regular feature, the next pandemic is around the corner, TB, HIV, and malaria are issues in the developed world, whilst non-communicable diseases such as cancer, cardiovascular disease, mental illness and diabetes take center stage in the agenda for developing nations, health reform is a national issues for the US, UK, China, emerging economies and low income countries... put simply all public health is global health.
With this in mind, it would be far more useful to concentrate on policy, economics, management, environmental health, epidemiology, biostatistics, the social determinants of health, health behavior change and education considering issues in a global context. Any school of public health worth its salt will challenge you to do this. I tend to advise people not to choose global health as their concentration and instead choose one of the core disciplines of public health to focus on. This will be much more useful and make you far more marketable upon graduation.
You will find there will be plenty of opportunities to do field trips abroad, to consider global health issues locally, to engage critically with these issues, to meet with like minded people in the field, and to take part in the plethora of student organizations and activities that consider global health, human rights, and humanitarianism. In fact, what you do outside the classroom is far more important that what you do inside. This is just one perspective (and I'm sure others will disagree) but I would urge all those considering global health to concentrate in one of the core public health areas with a global health gaze rather than to concentrate in global health.