The reasons for this widespread immigration throughout the 1990s are widespread, the fall of the Soviet Union, compounded with other Balkan problems such as the Yugoslav Wars led to widespread political unrest and political uncertainty not only in the Balkans, but throughout other former Eastern Bloc countries as well. The demography of the region is also of particular interest, both Greece and Italy, which have aging populations, attracted immigration from countries with a younger workforce, the push factor being the latter's inability to find jobs in their home country combined with Greece's need for cheap labour (especially in small scale family businesses, which are still prevalent). Another primary factor in this large scale rise in immigration is also the narrowing of the gap in terms of living standards between Northern Europe and Southern Europe, Greece has become, according to some, an attractive destination to economic migrants because of steady growth rates and EU member status - the presence of an informal economy that pays well has also added to this 'pull' factor in immigration trends, for example - An Albanian worker in Albania is paid on average $3 per hour, whereas he or she can earn anywhere from $6-$10 on average for working an informal sector job within Greece. Greece's large coastline and multiple islands mean that policing the entry of migrants has also become increasingly difficult, as Greece's reliance on Tourism has meant that borders have never been harshly policed (though this has begun to change as with the rest of the continent).
Chapter 3. Conclusion
Freedom of movement is often recognized as a civil right, the freedom only applies to movement within national borders: it may be guaranteed by the constitution or by human rights legislation. Additionally, this freedom is often limited to citizens and excludes others. No state currently allows full freedom of movement across its borders, and international human rights treaties do not confer a general right to enter another state. According to Article 13 of the Universal Declaration of Human Rights, citizens may not be forbidden to leave their country. There is no similar provision regarding entry of non-citizens. Those who reject this distinction on ethical grounds, argue that the freedom of movement both within and between countries is a basic human right, and that the restrictive immigration policies, typical of nation-states, violate this human right of freedom of movement. Such arguments are common among anti-state ideologies like anarchism and libertarianism. Note that a right to freedom of entry would not, in itself, guarantee immigrants a job, housing, health care, or citizenship.
Where immigration is permitted, it is typically selective. Ethnic selection, such as the White Australia policy, has generally disappeared, but priority is usually given to the educated, skilled, and wealthy. Less privileged individuals, including the mass of poor people in low-income countries, cannot avail of these immigration opportunities. This inequality has also been criticized as conflicting with the principle of equal opportunities, which apply (at least in theory) within democratic nation-states. The fact that the door is closed for the unskilled, while at the same time many developed countries have a huge demand for unskilled labor, is a major factor in illegal immigration. The contradictory nature of this policy - which specifically disadvantages the unskilled immigrants while exploiting their labor - has also been criticized on ethical grounds.
Immigration polices which selectively grant freedom of movement to targeted individuals are intended to produce a net economic gain for the host country. They can also mean net loss for a poor donor country through the loss of the educated minority - the brain drain. This can exacerbate the global inequality in standards of living that provided the motivation for the individual to migrate in the first place. An example of the 'competition for skilled labor' is active recruitment of health workers by First World countries, from the Third World.
References
1. Immigration to Greece during the 1990s: An Overview, Maria Siadama;
2. 
Michael Sauga. Skilled Immigrants? No Thanks August/ Spiegel Online International, 29, 2007 https://www.spiegel.de/international/business/0,1518,502786-2,00.html;
3. Official report on Spanish recent Macroeconomics, including data and comments on immigration;
4. Roger Cohen. Globalist: On French immigrants, the words left unsaid/ Herald Tribune International, NOVEMBER 11, 2005 - https://www.iht.com/articles/2005/11/11/europe/web.1111globalist.php;
5. Wikipedia: The free encyclopedia - https://www.wikipedia.org