In fact, Ramadan is a chance for the Muslim Ummah to step forward towards unity, even in some rituals and acts of worship. Ramadan is a golden chance to purify our hearts and unite our efforts.
Coming to the core point of your question, there is a difference among Muslim scholars whether all Muslim countries should start fasting when the new moon of Ramadan is sighted in a Muslim country or should each country follow its own sighting of the new moon.
a great number of Muslim scholars prefer the opinion which says if the new moon of Ramadan is sighted beyond doubt in a given country, all other countries, which share part of the night with it, should start fasting.
If Muslims all over the world fail to achieve this unity in rituals such as fasting, `Eids, etc., then each Muslim community is required to observe its unity in this regard. It is not acceptable at all for Muslims in a single community to divide over the beginning and end of Ramadan. The dilemma of the Muslims in the West is that some Muslims follow the sighting of the Saudi Arabia or other Islamic countries while others follow the sighting of their locality. Members of the same community should be united in this regard and Imams of the mosques should observe unity in the beginning and end of the fasting.
In this regard, the late Syrian scholar Dr. Mustafa Az-Zarqa, states: According to the views of the majority of scholars and jurists, if the new moon of Ramadan appears in the East first, people living in the West should abide by it, and vice versa, in order to agree on the day to commence fasting. This is because the interval that occurs between the appearance of the new moon in a country or another is rather slight, and therefore there is no need to consider it.

I have actually been informed that Muslims in Western countries, especially in different cities of America, like Houston and New York, do not start fasting on the same day, despite being in the same country. Some follow the astronomic calendar according to their location; others follow Saudi Arabia; and some others consider Sha`ban as a 30-day month (i.e., they fear fasting one day early), and this is not at all acceptable in one country.

Moreover, Sheikh Ahmad Kutty, a senior lecturer and an Islamic scholar at the Islamic Institute of Toronto, Ontario, Canada, adds: This is an issue that must be decided by the collective body of scholars and leaders representing Muslims in this part of the world. Traditionally, in fiqh (Islamic jurisprudence) there are two valid interpretations on this issue: According to the first view, which has

been considered as the most authentic and preferred view in the Hanafi school (as stated in al-Fatawa al-Hindiyyah), if the moon is sighted in the East, it is binding on the West, provided they can act on such information; the second view, however, states that each region should sight its own moon.
It is therefore up to the Muslims in this part of the world to choose any of the above views; they should do so based on the best interests of the Ummah in this part of the world.
Individuals, however, must never take this issue in their own hands; rather they must abide by the decisions of the collective leadership. The Prophet (peace and blessings be upon him) advised us to follow the Jama`ah (Muslim community); so we must not divide Muslims on this issue based on our own individual preferences.