Masada on definition of genocide said:
(e) Forcibly transferring children of the group to another group.
During WW2 over 200,000 Polish children were kidnapped from parents and transported to Germany to be adopted by German parents and raised as Germans.
As also
Traitorfish mentioned, genocide does not necessarily consist of physical extermination of individuals (i.e. a collection of a very large number of murders is not necessarily a genocide), but it is all about erasing a peoples or a nation, a race, a religious group, or an ethnic group
as a community.
Genocide is derived from Greek word "genos", which means: nation / kind / race / ethnos / stock / tribe.
Therefore genocide is an attempt to eliminate a community such as these ones mentioned above.
Therefore not only German crimes against Poles, but also Soviet policies of exterminating certain elites of the Polish nation should be considered as genocide, because exterminating elites of a nation inevitably leads to disintegration of such a nation as a community, and transforms it into just a collection of individuals which can be easily denationalized or absorbed by another nation. Forcible assimilation can also be element of a genocide.
Hitler also did not intend to physically exterminate all Polish (or Slavic in general) people, he wanted to exterminate all nation-building elites as well as those simple individuals who were "racially unsuitable" according to his own arbitrary criteria, while the rest of simple Slavic individuals were to be turned into stray biological material and then recycled in ethnic sausage machines, eventually being turned into Germans (i.e. Germanized):
http://forums.civfanatics.com/showthread.php?p=13299846#post13299846
We can say that some of International Communists wanted to commit genocides against all existing nations, since they wanted nations to disappear.
Internationalist Communists didn't want to physically exterminate all people, but they still wanted their national & ethnic identities to disappear.
Of course persecution and physical extermination of selected individuals such as "nationalists", "Whites", or "patriots" was part of achieving that goal.
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The Nazis also wanted nations and ethnic groups to disappear - whether through assimilation into Germans, or through physical destruction.
Heinrich Himmler wrote this n 28 May 1940 (at first, the Nazis wanted to fragment the Polish nation - citizens of Poland - into many groups hostile to each other; after that they wanted to "deal" with each group separately, in turn, either by physical extermination, expulsion, assimilation, etc. -
regardless of means applied, the ultimate goal was to be the same in each case: disappearance of each group as an ethno-cultural-religious community):
... We must take care for the largest possible amount of national groups. Not just Poles and Jews, but also Belarussians, Ukrainians, Highlanders, Kashubs and Lemkos... It is important for us not to deal with one, unified nation, but it is in our interest that this nation is fragmented into plenty of individual, small parts. We must prevent any consolidation of national culture between those parts, because our goul is to crumble those people into countless fragments... We need to disintegrate into shapeless mass 15 million population of the General Gouvernement and 8 million in new eastern provinces of the Reich...
... In several years from now, perhaps no more than 4 or 5, the - for example - Kashubian issue shall no longer exist - as there will be no trace of Kashubians... The same refers to Masurians... I also expect that the word "Jew" will disappear completely, thanks to deportation of all Jews to Africa... After just a bit longer time we shall be able to also completely remove from our territories all memory of such tribes like Ukrainians or Highlanders... The same in broader terms will also concern the Poles...
... For non-German population in eastern territories there should not exist any school higher than four-class primary school. Education programme of these communal schools shall include the knowledge of counting to 500, not higher. It shall also teach children the principles given by God: submission to Germans, necessity of being honest, hard-working and brave. I do not - on the other hand - consider as necessary to teach them reading... Apart from this type of schools no other ones can exist in the East...
... Parents wanting better education for their children will be obliged to send a proper request to local SS or Police authorities. If their children represent a desirable racial type, they will be evacuated to Germany for education, they will be given new surnames and they will stay there forever... Parents of such children must either disclaim them - and probably as the result also resign from having further progeny, which will remove the danger of this subhuman nation breeding types with leadership skills - or emigrate to Germany, in order to, after changing their surname, enter the German world. But caution and supervision will still have to be applied regarding such parents...
... After systematic operations, only population consisting of just subhuman elements will remain in the General Gouvernement. This depersonalized, deprived of their identity mass of people will become a human resource, designed as laborers for construction projects in Germany...
... Deprived of culture, under severe, consistent and righteous leadership of the German Nation Poles will participate in the task of creating eternal cultural values, such as the construction of monuments and great buildings. Regarding the latter ones, they will repeatedly enable their creating, providing necessary amounts of labour force..."