I have this HTML:
North America
Your code will just place html in the last div within #region_North_America. Use the append function.
$("div.region-list").append(row_str);
Or:
$("<div>content here</div>").appendTo("#region_North_America");
To create the element on the fly, and place it in the document.
Using the appendTo method.
Try:
$("#region_North_America").append(row_str);
using append().