Kafawa da faɗaɗa ƙasar Poland a cikin karni na 10 ana iya komawa zuwa Polans, ƙabilar Slavic ta Yamma wacce ta zauna a yankin Greater Poland, ta amfani da mahimman wurare na Giecz, Poznań, Gniezno, da Ostrów Lednicki.A farkon karni na 10, an fara gagarumin katangawa da fadada yanki, musamman a kusan 920-950.Wannan lokaci ya kafa hanyar juyin halittar waɗannan ƙasashe na ƙabilanci zuwa wata ƙasa mai ƙarfi a ƙarƙashin jagorancin daular Piast, musamman Mieszko I.Mieszko I, wanda Widukind na Corvey ya fara ambata a cikin kafofin zamani a tsakiyar 960s, ya yi mahimmancin siffa ta farkon ƙasar Poland.Mulkinsa ya ga rikice-rikice na soja da haɗin kai, kamar aurensa a shekara ta 965 zuwa Doubravka, gimbiya Kirista Bohemian, wanda ya sa ya tuba zuwa Kiristanci a ranar 14 ga Afrilu, 966. Wannan taron, wanda aka sani da Baftisma na Poland, ana daukarsa a matsayin tushen tushe ga kasar Poland.Mulkin Mieszko kuma ya nuna farkon faɗaɗa ƙasar Poland zuwa yankuna kamar ƙaramar Poland, ƙasashen Vistulan, da Silesia, waɗanda ke da haɗin kai wajen samar da yanki mai kusan Poland na zamani.Polans, a ƙarƙashin mulkin Mieszko, sun fara ne a matsayin tarayya na kabilanci kuma sun samo asali zuwa wata ƙasa mai tsaka-tsaki wadda ta haɗu da sauran kabilun Slavic.A ƙarshen karni na 10, daular Mieszko ta mamaye wani yanki mai faɗin murabba'in kilomita 250,000 kuma yana zaune a ƙasa da mutane miliyan ɗaya.Yanayin siyasar ƙasar Poland ta Mieszko ya kasance mai sarƙaƙƙiya, wanda ke tattare da ƙawance da kishiyoyi a yankin.Dangantakarsa ta diflomasiyya da Daular Roma mai tsarki, ta hanyar kawance da haraji, ta kasance mai matukar muhimmanci.Haɗin kai na soja na Mieszko tare da kabilu da jihohi maƙwabta, irin su Velunzani, Slavs na Polabiya, da Czechs, sun kasance masu mahimmanci wajen tabbatarwa da faɗaɗa yankunan Poland.Yaƙin Cedynia a 972 da Margrave Odo I na Saxon Gabashin Maris babban nasara ce da ta taimaka wajen ƙarfafa ikon Mieszko akan yankunan Pomerania har zuwa Kogin Oder.A karshen mulkinsa a wajajen shekara ta 990, Mieszko ya kafa kasar Poland a matsayin babbar kasa a tsakiyar gabashin Turai, inda ya kai ga mika kasar ga hukumar mai tsarki ta hanyar Dagome iudex daftarin aiki.Wannan aikin ba wai kawai ya ƙarfafa halin Kiristanci na jihar ba har ma ya sanya Poland da ƙarfi a cikin faffadan siyasa da addini na Turai.