Each city was independent of each other. Even under Alexander the Great, each city contributed soldiers to the common cause, yet did not accept the central government that the later Romans did. The Greeks were loyal to a particular city, not to a particular country. So, when a concerted attack happened, each city fell as a unit, not the whole country. Instability occurred when there was no political unity.
Each state in ancient Greece had its own government. The geographical features of Greece with its many mountainous islands could not be united. The city states were split from each other by nature's boundaries. The topography of the country also added to this.
The Greeks established themselves on tracts of land in between mountains and built cities as the centre of their land. This led to separate city-states - about 2,000 of them, each with heir on government. With this independence, the city-states were not about to give it up to become subject to another city, and were prepared to fight to remain so. They formed alliances and leagues, which changed from time to time according to the self-interest of the cities.
Their other connections were religious in the form of games - Olympic, Nemean, Isthmian etc, and a religious council to coordinate sacred matters.
Originally, it had much to do with Greece's geography: almost 80% of Greece is covered by mountains, which at the time were covered with dense forests. All this made communication in ancient times very difficult. Moreover, the areas with flat and arable land were few and far between; the posession of 'good' land was much more a source of conflict and rivalry than a reason for unity. The result: if Greek States did unite for a period, it was usually just to better beat the crap out of another Greek State.
Even Alexander the great - although he directly or indirectly ruled all the Greek States - never managed to unite them, and it would take until the arrival of the Romans before Greece was more or less ruled as one State.
Because the huge empire was so big that it was hard to control with just one person.
Threat of annihilation by the Persian invasion
It did not unite various interest groups.
They did not unite the Greeks - there was just a pause in their fighting each other while the games were on.
Originally the reason the Greeks founded the Olympics was to have a "family reunion". At the time, Ancient Greeks were scattered from Spain to North Africa, and from Ionia to Italy. This was a way to unite themselves every 4 years. Eventually it turned into a "which colony is the best" competition, and the model that we have today.
I think it unite in 1932
because the sperm cells fail to find the egg cells or the sperm isn't good to unite with the egg
Spina bifida means a congenital condition in which the lamina fail ut unite at midline.
Threat of annihilation by the Persian invasion
Here we go...
Most rational people think they fought them.
Staging something serving
It did not unite various interest groups.
They established independent city-states, and like the Greeks, had no reason to give up their independence.
To more or less unite them in the "Hellenic League" that would have him as overlord.
His father had a dream to unite the city-states. Shortly after he died so Alexander was his heir. Alexander took his father's dream and tried to unite the Greeks, the Persians, and the Macedonians. He failed
Those who fail to learn from past history are doomed to repeat it.
The German kings faced challenges such as internal divisions among regional princes, opposition from the papacy, and resistance from powerful nobles, which hindered their efforts to unite Germany under strong centralized rule. Additionally, the decentralized structure of the Holy Roman Empire allowed for a significant degree of autonomy among its member states, making it difficult for any single ruler to assert control over the entire territory.