Feel free to post quotes from this book that state "all" of Eastern Germany was settled by Slavs.
Check Eric Christiansen, "The Northern Crusades", read the following chapters (I'm not going to quote entire chapters!):
1. North-East Europe on the Eve of the Crusades
Land and Sea
Peoples
Interactions
2. The Wendish Crusade in Theory and Practice, 1147-1185
The Crusade of 1147
Supporters and Chroniclers
The Slav Wars of Henry the Lion and Valdemar the Great
DNA results do not tell you your race or your specific ancestors.
You are wrong. This is exactly what DNA tells - because people inherit 100% of their DNA from their ancestors.
And IBD segments (IBD stands for Identical By Descent) of your DNA can tell a lot about your ancestors:
http://www.isogg.org/wiki/Identical_by_descent
If you share IBD segments with another modern peoples or with an ancient specimen, then you are related.
You can't be meaning "all" in the literal sense of the word. Parts of Poland were settled by Germanic tribes, as well as other tribes such as the Scythian tribes, Celtic tribes and Baltic tribes. So what? Slavs settled in Poland since the second half of the 5th century. Poles are Slavs. Poles come from the Polish tribes that settled in Poland.
This is a similar case as with English people. We know, that they are mostly Celtic. So why are you assuming that Poles are entirely (or even mostly) Slavic? As you've noticed, other peoples lived there before Slavs - just like other peoples lived in England before Germanics. Neither in England nor in Poland those peoples disappeared completely, but rather partially got assimilated and absorbed by newcomers.
Of course archaeologists observe depopulation (suggesting a drop in pre-Slavic inhabitants), but - on the other hand - they do not observe signs of massive immigration. Rather, a gradual influx of small Slavic groups from the east. So while local pre-Slavic population declined sharply in numbers, newcomers were also not numerous - so it is not certain, in what exact proportions the two groups mixed.
Generally - it is obvious that Poles are both Slavic and Germanic - but exact proportions of each ancestry can be disputed.
Substrates (= assimilated previous populations) have been detected in genetic research on Slavs.
What proves that these substrates were absorbed by Slavs is that today North Slavs are genetically closer to their Non-Slavic neighbours (such as Lithuanians, Germans, Finns, Mordvins, Udmurts, etc.), than they are to South Slavs - who in turn are closer to their Non-Slavic neighbours (such as Romanians, Albanians and Northern Greeks). Let's post some quotes from a 2015 study on Slavic ancestry:
"(...) Several mechanisms including cultural assimilation of the autochthonous populations by expanding Slavs while maintaining the pre-Slavic genetic boundaries, and in situ gene pool shaping, are needed to explain the genetic patterns observed on the eastern, north-eastern and western margins of the current ‘Slavic area’ within Central-East Europe. The presence of two distinct genetic substrata in the genomes of East-West and South Slavs would imply cultural assimilation of indigenous populations by bearers of Slavic languages as a major mechanism of the spread of Slavic (...)"
And:
"(...) The data suggest that genetic diversity of the present-day Slavs was predominantly shaped in situ, and we detect two different substrata: ‘central-east European’ for West and East Slavs, and ‘south-east European’ for South Slavs. (...) The importance of these substrata in shaping the genetic diversity of the present-day Slavs is evident from the observed lower IBD relatedness between the combined group of East-West Slavs and South Slavs than with north-east Europeans, including Baltic speakers (Fig 4A). The latter reside within the East European Plain and presumably represent the “central-east European” pre-Slavic substratum (Fig 4A, Table G in S1 File). AMOVA results also support the substrata prevalence, because genetic variation among Slavic branches (which assimilated different substratum populations) strongly exceeds intra-branch variation (...)"
And:
"(...) In addition, age estimates for major paternal and maternal lineages of East-Central Europe point to an expansion that pre-dates the historic spread of Slavs. For example, whilst the geographic distribution of NRY haplogroups (hg) I-P37 and R1a-Z282 overlaps with the area occupied by the present-day Slavs, coalescent times suggest that the current diversity within these hgs existed prior to the Slavic expansion [29,35]. Similarly, the phylogeography of mtDNA hgs that are more frequent in West and East Slavs–such as H5a1, U4a2, U5a2a, U5a2b1 –suggests continuity within East-Central Europe for at least two thousand years [28,36–38]. (...)"
This study also found out, that when it comes to similarities between Slavic and Germanic groups, Poles and Sorbs are closer to Swedes than to Germans, while Czechs and Slovaks are closer to Germans than to Swedes. What does this suggest? This suggests that Poles and Sorbs have more ancestry from East Germanic tribes (such as Goths) - who were closer to Scandinavians - while Slovaks and Czechs absorbed Celts and West Germanic groups living to the south of the Carpathians-Sudetes. And modern Germans also are largely Celtic.
There is a world of difference between DNA results showing racial clusters and determining one's race.
No, it is you who has some kind of archaic / strange view on what is race. Tell me please how do you define race - can you do this ???
You cannot use any random trait, such as hair color or height. For example, redheads are not a separate race from blondes.
One of my uncle and aunt have 2 daughters, one is red-haired the other one is black-haired, they also look differently in terms of anthropological types, but I can't say that they are two distinct races - it would be ridiculous. They share both parents in common.
"Stupid French people" are also not a separate race from "smart French people", because they are the very same reproductive community. You can even have one dumber sibling and one smarter sibling in the same family, because inheriting intelligence works in such a way, that there can be differences between siblings. Only identical twins tend to be very similar in this respect, but other siblings can differ a lot.
"People with hooked nose" are not a separate race from "people with straight nose", as long as their genetic cluster is the same.
You can't be meaning "all" in the literal sense of the word.
By all parts of East Germany I meant that Slavs became the exclusive inhabitants of that area - that is, all inhabited lands (those which were not wilderness), were inhabited by Slavic-speakers. Whatever left of pre-Slavic population, was assimilated (Slavicized).
There is no evidence of Germanic continuity and survival of Germanic-speaking groups from ca. 500 AD until ca. 1200 AD.
After 1200 AD Germanic language was re-introduced there by migrants from West Germany. But it was a different language - it was a West Germanic language, while in Ancient times those areas were inhabited by East Germanic and Elbe Germanic speakers.
So it would be like colonizing Slovenia with Russians, and saying that it is a continuity of Slavic speakers.
There are words which carry the presage of defeat. Defence is such a word. What is the result of an even victorious defence? The next attempt of imposing it to that weaker, defender. The attacker, despite temporary setback, feels the master of situation.