You may also read Chapter 13 of Kurosh's book. For instance, it contains a proof of Baer's theorem (cited by @Igor) which says that

all p-Sylow subgroups of a locally normal group are isomorphic.

Locally normal means periodic with finite conjugacy classes.

You may also read Chapter 13 of Kurosh's book Theory of groups, volume 2. For instance, it contains a proof of Baer's theorem (cited by @Igor) which says that

all p-Sylow subgroups of a locally normal group are isomorphic.

Locally normal means periodic with finite conjugacy classes.

You may also read Chapter 13 of Kurosh's book. For instance, it contains a proof of Baer's theorem (cited by @Igor) which says that

all p-Sylow subgroups of a locally normal group are isomorphic.

Locally normal means periodic with finite conjugacy classes.

You may also read Chapter 13 of Kurosh's book. For instance, it contains a proof of Baer's theorem (cited by @Igor) which says that

all p-Sylow subgroups of a locally normal group are isomorphic.

Locally normal means periodic with finite conjugacy classes.