Replacement theology, also called Supersessionism, is the false teaching that the Body of Christ/Church has replaced the nation of Israel regarding the plan, purpose and promises of God. They teach that Israel is no longer God's chosen people, instead the Church has replaced them. This view is far from Biblical. Those that believe this false doctrine will often go to Romans 11 to prove their heresy.
Romans 11:1 "I say then, Hath God cast away his people? God forbid. For I also am an Israelite, of the seed of Abraham, of the tribe of Benjamin."
In the above verse, the phrase "his people" is a reference to Israel, not the Church or "spiritual Jews". We know this because Paul gives his genealogical credentials. This verse is talking about the physical Israel and the physical tribes of Israel. Paul labels himself an Israelite and also calls himself a Jew by nature in Galatians.
Galatians 2:15 "We who are Jews by nature, and not sinners of the Gentiles,"
Every time the phrase "his people" shows up it will be a reference to the nation of Israel more than 90 percent of the time.
Deuteronomy 7:6 "For thou art an holy people unto the LORD thy God: the LORD thy God hath chosen thee to be a special people unto himself, above all people that are upon the face of the earth."
Exodus 3:7 "And the LORD said, I have surely seen the affliction of my people which are in Egypt, and have heard their cry by reason of their taskmasters; for I know their sorrows;"
Exodus 3:10 "Come now therefore, and I will send thee unto Pharaoh, that thou mayest bring forth my people the children of Israel out of Egypt."
Exodus 8:1 "And the LORD spake unto Moses, Go unto Pharaoh, and say unto him, Thus saith the LORD, Let my people go, that they may serve me."
Exodus 19:5 "Now therefore, if ye will obey my voice indeed, and keep my covenant, then ye shall be a peculiar treasure unto me above all people: for all the earth is mine:"
Note: As Christians, we are to bless Israel. It would be wise to stay away from the conspiracy THEORIES about the Jews. Many physical Jews are located in Israel today. The government in Israel is not perfect (no government is), but it is not our job to put them down because America along with every other nation, besides Israel, is "as a drop of a bucket" (Isa. 40:15). Let us leave the judgment to God because God is very consistent with judging those that curse Israel. Any serious Bible Believer should be Pro-Israel.