Yes ! It is possible to zoom to specific country or state or city.
MKMapView provides such zooming functionality.
So, for zooming to specific location, one must know left-lower-co-ordinate of that location & right-top-co-ordinate of that location.
For example, we are assuming that we have to zoom to USA country. Please go through comments within the code to understand it.
// lower-left co-ordinate of USA MAP
CLLocationCoordinate2D lowerLeftCoOrd = CLLocationCoordinate2DMake(21.652538062803, -127.620375523875420);
// create a map-point using lower-left co-ordinate.
MKMapPoint lowerLeft = MKMapPointForCoordinate(lowerLeftCoOrd);
// upper-right co-ordinate of USA Map
CLLocationCoordinate2D upperRightCoOrd = CLLocationCoordinate2DMake(50.406626367301044, -66.517937876818);
// create a map-point using upper-right co-ordinate
MKMapPoint upperRight = MKMapPointForCoordinate(upperRightCoOrd);
// create a map-rect using both co-ordinates as follows.
MKMapRect mapRect = MKMapRectMake(lowerLeft.x, upperRight.y, upperRight.x - lowerLeft.x, lowerLeft.y - upperRight.y);
// set zoom to rect & you are done.
[self.mapView setVisibleMapRect:mapRect animated:YES];