Inner join with if condition satisfies

I want to inner join only if my condition satisfies. In the given code my if condition is failing. I'm new to stored procedures. Can anyone help me with how I can write if condition based on my request? Thanks in advance.

INNER JOIN 
IF(@Country IS NOT NULL) OR (LEN(@Country) > 0)
BEGIN
(SELECT A, s.B, s.C, s.D, sv.D FROM  [AM].[dbo].[XYZ] s
INNER JOIN [PM].[dbo].[ABC] sv
ON s.A = sv.D collate SQL_Latin1_General_CP1_CI_AS where Country= @Country) TABLE
ON RO.OByID = TABLE.Id 
END
ElSE 
BEGIN
INNER JOIN Table2 ON RO.OByID = Table2.Id
END

INNER JOIN (GTGTG)
INNERJOING(GDGF)

...Etc