By viviting Myanmar, Obama has sent a message that democratic changes with respect for human rights will be rewarded by the USA, and by visiting Cambodia, he has formally welcomed thsi country into the fold with the same message of rewards for democracy.
This is China's backyard and the USA is announcing that they will trade and otherwise interact with these countries . China has recently had a change of leadership and it was very important for the USA to send these messages, and send them early.
China has recently been engaged in land disputes with Japan and also with Taiwan, Vietnam and the Philippines and the USA has to show that itis aware and is engaged. This has to be clearly stated and Obama has done so with his visit. Myanmar has had a close relationship with China but has been moving away partly because of the Chinese exploitation of its resources. Now with the relaxation of dictatorial rule, the freeing from house arrest of Aung San Suu Kyi and the recent election, it has brought an easing of embargo and an opening for trade with America and the West
Obama's trip is also a sign that the USA has moved intellectually, economically, militarily and diplomatically from the West/Europe with its weakened economy/ state structure/ aging population and thus clout, to the East with its growing economy, literate population and thus clout. It is China, India, Indonesia, Australia and yes Japan and still Taiwan, Korea, the Phillipines, Malayasia and Singapore. This is where the action will be for the next years, growing by leaps and bounds . Not only trade for resources but also intellect, even as Europe was 60 years ago.
Europe could not rebound from the loss its colonies, whose resources (they were so reliant on) kept it going. These countries (France, Britain, Italy, Spain etc) would not adapt and change to meet the changing times and demography, and they lacked the leadership who were more prone to look inwards than outwards and failed to utilise the intellectual resources of those who were different but who were part of them but not fully so. The USA on the other hand has shown time again that with visionary leaders it can re-invent itself and remain relevant and strong. As President Obama (to make a point about accepting changes) pointed to his skin colour, (in Myanmar) to show what could be accomplished with tolerance, acceptance and inclusion.
There is one pitfall the USA has to avoid. Understand the culture, the values, the beliefs, the idiosyncrasies of those with whom you will deal. Bowing and putting hands together and not handshakes or kissing cheeks. It is so much more polite and decorous and less clammy/sweaty and oh, don't forget to take off your shoes when entering Holy places. Leave the detritus and your "ugly" attitude behind or you will screw it up. Namaste. Salaam, Ni Hao, Arrigato y'all.