First of all, we’d like to stress that Muslims should try their best to achieve their unity in all aspects, not only in the beginning and end of Ramadan and celebrating the `Eids. It is against the spirit of Islam to see Muslims in the same country divided in their rituals and their Islamic dates and events. The Islamic spirit is against division and disunity.
The new moon is difficult to sight and may be invisible due to atmospheric conditions. It can appear on different days in different countries, especially when two countries are very far apart. Ramadan (and the other Islamic months, as well) must be a minimum of 29 days. Thus, those countries that started Ramadan a day or two days after the others will also celebrate `Eid Al-Fitr one or two days later than others. They cannot have a 28-day month.
Regarding the dates of the beginning and end of Ramadan, a Muslim should follow the decision of the Muslim authorities in the country of his residence. It is not his concern what others, especially those on the other side of the globe, do.
Responding to this issue, Sheikh Ahmad Kutty states the following:
In such matters of this nature, a Muslim should follow the decision of the congregation, for the Prophet (peace and blessings be upon him) is reported to have said, “Fast with people, break your fast (i.e., celebrate `Eid Al-Fitr) with people, and celebrate sacrifice with people.”
So we are not to make such kinds of decisions based on our own personal preferences or inclinations.
Based on this, if you are living in the USA you must follow the decisions of the Muslims there; if, on the other hand, you are living in another country, then you must go by their decisions.
We should not be creating dissensions in the community on this issue. Let us seek to focus instead on far more important issues that are crucial for the survival of Muslims in this time and age.