You may be right that sikkim was an indiapendent state but so were the other states of INDIA and they were merged into one country after independence. If India had not done that then others would have. China had captured, as everybody know around 500,000 sq KM of Indian Northern territory even after integeration of all the scattered states into one country, INDIA. That was invasion. Not that the Sikkim involvement in India. That's integeration of the states which are aloof and cornered. I believe, in today's international political situation no small and free state can be independent in its decison making and would be trickling down the economical graph and overall growth of the country. Look at burma, myanmar and other small patches on world map. They are almost exploited and destined to loose the race with the big fishes like china and othe neighbouring expansionist. So I believe inclusion of Sikkim in India was iminent otherwise China was always looking at it and I believe even now is in her sight.
When author said India should act before maoist take over Nepal doesn't really mean to capture but to capitalise on the borders to maintain there integrity.
